The main window is split into simple sections, some of which will be familiar from other applications. In fact, as we introduce the components of the window you'll see DEVONthink has many familiar elements in it. We start off with the fundamental panes you'll use.
When you open a Finder window, you are presented with a list of files in a certain location. The view may be icons or a list, etc. but you are still just viewing the contents of a folder, hard drive, etc.
DEVONthink is no different in this respect. When you open a main window, you will see a list of groups and documents in the current location. Clicking on or opening other groups shows their contents. Smart groups, just like the Finder's smart folders, also display their contents in an item list. The item list also supports familiar operations like drag-and-drop between groups, copy and paste, group and ungroup, context menu items when you Control-click, etc., just as you've done in the Finder.
Views: Again, taking a cue from the Finder, the item list allows you to display your documents in some familiar views:
Icon view. This displays the thumbnails of the documents with just their name. If you enable View > Show Details, it will display some additional metadata about the documents. This is normally used in a Standard view or with the View/Edit pane hidden. You can change the size of the thumbnails with the slider in the information bar below the toolbar. However this will affect the amount of metadata shown as well if the details are shown. Double-clicking groups behaves just as double-clicking a Finder folder, displaying the contents in the current or a new window, depending on the Double-click opens groups in a new window checkbox in General > Interface settings.
List view shows a list view of the items with metadata columns. Sort them by clicking the column headers, switching between ascending and descending each time you click. Drag the columns left and right to reorder them to your liking. Add and remove columns by Control-clicking and choosing headers or toggling them in the View > List Columns submenu.
Columns view functions in the same way as the Finder, displaying sibling items in columns. For example, selecting a group shows its contents in the next column. If you use View > Show Details, a column appears to display metadata and the document's thumbnail. You can resize the width of columns by dragging the separator line between them. Double-clicking the separator expands the column to the width of the widest title and holding the ⌥︎ Option key expands all columns. To make this easier you can set macOS' System Settings > Appearance > Show scroll bars to Always. This view typically works best with a preview in Standard layout as the item list's width in Widescreen usually only shows the current column.All these views can be easily changed in the View > View options, as well as the trio of icons on the right-hand side of the Information bar.
Sort: In addition to sorting the item list by clicking column headers or using the View > Sort menu, you can also choose a sort method in the Sort dropdown menu in the information bar. The default is sorting by Name. If you feel there are too many options available, choose Customize Metadata in the View > List Columns > Customize Metadata, the context menu, and this button. A panel opens listing all the available properties. Toggle the options you want to be able to choose as a sort method.
DEVONthink provides some visual cues applied to items in the item list. These are also described in the Iconology section of the Appendix.
Duplicates and Replicants:
icon, depending on your setting in Settings > General > Mark duplicates and replicants in color.
icon, again depending on the preference setting.Files with Attributes:
Files with Links:
Marked files are ones with item attributes found in the Data > Mark menu. In List and Columns views, the property icons will not be shown unless the Flag option in View > List Columns is enabled.
Marked Files:
Enabled in the View > List Columns menu, the Flag column shows the state of an item: 
flagged or unflagged, or the 
unread status of items. Clicking in the flag column toggles the flagged state. If an item is unread, a circle will appear in this column. If you have a group containing a mix of flagged and unflagged items, a dash will appear in this column, showing an indeterminate state.
As illustrated above, DEVONthink displays special property icons to the right of item names for attributes like Finder Comments, reminders, etc. A key of the property icons is in the Iconology section of the appendix.
Context menu: The available context menu commands depend on the current selection in the item list. As there are many commands, they are described separately in the Context Menu > Item List section of the Appendix.
When You launch DEVONthink you will see an empty pane at the bottom of the window reading Nothing Selected. This is the View/Edit pane, a core element in the interface you will likely use very often. This pane is where you can view documents and edit compatible formats, e.g., rich text. You can also view the documents in a selected group if you have Behavior: Preview group content enabled in the General > Interface settings. You can can toggle the pane's position or visibility in the View > Preview menu or via a toolbar button. The menu options are:
Layouts:
As noted above, DEVONthink allows displaying and editing, and even creating, some file types. Please refer to the Documents chapter for more information on this and other components related to the View/Edit pane.
At the top of most Mac applications you encounter, including the Finder, you will see the toolbar. For people who prefer working with tracking devices, e.g., mice, trackpads, etc., the toolbar allows you to have quick access to some functions without having to go through the menus. DEVONthink also provides a toolbar in main and document windows.
The toolbar comes pre-installed with a handy default set of buttons, including the search field (see below). It can be customized via Tools > Customize Toolbar command or in the context menu of the toolbar. Add, remove, and reorder these items to suit your particular needs. On a side note that also applies to Finder windows, if you want to quickly reorganize items on the toolbar, hold the ⌘︎ Command key and drag the item to its desired location, or off the toolbar to remove it.
If you're looking for a little more space for your toolbar, or even a little less, you can choose to display the toolbar as Icon and Text, Icons Only, or Text Only. If you choose Icon Only, the current selection's database and name will not appear. And if you want to go fully minimal, View > Hide Toolbar hides the it completely.
You will find a list of the available toolbar items is available in the Toolbar section of the appendix.
In some applications, extra information about files is shown in a pane on the right side of a window. DEVONthink has several inspectors providing a wide range of information and commands, separated into related views. For example, data about the name, tags, type, etc. of a selected file are available in the Generic Info inspector. The various inspectors are gathered into one pane displayed on the right side of main and document windows alike, especially helpful on smaller screens.
The inspectors are individually discussed in the Inspectors chapter.
Storing information is a useful thing, but it's more useful when you can find things too. DEVONthink offers a strong search function for finding items in your databases, all integrated into a main window.
In the toolbar is a search field for entering your search terms. Type in a word and the search pane appears showing any matched items — and yes, it's another item list supporting the different views and sort methods discussed above. If the View/Edit pane is open, it will display selected result. For contents-based searches, the search terms will be highlighted in the preview, whenever possible.
Search options: In the search field, you will notice a 
magnifying glass icon. Click this icon to see where to search, list the ten most recent search queries, one choose among the following options:
sync*, matching "synchronize" or "syncing" but not "resync". Enabling this option also activates Live while typing so the results dynamically change as you type. Press the ↩︎ Return key to treat the last term as a complete word.hello and hullo would be matched.text:fish the matching documents would likely also highlight various species mentioned. Note this option will not work with Partial matches while typing and Fuzzy Word Comparison enabled. Also, smart groups do not support this option.There is also a hidden preference, EnableSearchFieldAutocompletion, to allow DEVONthink to try to automatically complete words you're typing. However, this option only works when the search options Live while typing and Partial matches while typing are disabled.
Search prefixes: Anything you type into the search field will be treated as searching in all possible attributes. However, if you want to focus on specific attributes, e.g., file types or tags, the search field supports prefix operator searches, similar to Spotlight. Common examples are searches like name:DEVON or tags:tech;sync, separating multi-valued attributes like tags with a semicolon. There are a wide variety of prefixes available, as well as different prefix operators. A complete list of these items is included in the Search Prefixes section of the appendix.
In addition to search prefixes, DEVONthink supports Boolean operators, parenthesis for grouping terms, and quotes to match specific terms. Read more about operators and how to use them in the Search Operators section of the appendix.
Search scopes: After you've done a search, you will also see a bar above the search results allowing you to choose the scope of the search. The scope specifies "where" you're searching. You will be shown All Databases, Inboxes, the name of the current database, and the name of the current group, if you're currently viewing one. Choose one to expand or limit where DEVONthink is searching. For quickly switching scopes with a keyboard, hold the ⌥︎⌃︎ Control keys and press 1 through 4 while a search is active. If you are searching in a particular location and want to ignore possible matches in the subgroups, enable the Exclude Subgroups checkbox, as needed.
Advanced searching: To the right of the search scopes, click the 
button to open the predicate editor, similar to what is used in smart groups and smart rules.
If you have done a search you'd like to use again, press the Save button. Enter a name and DEVONthink will create a smart group for you. If your search scope is in a group, the smart group will be created there. If you are searching a specific database, the smart group is created in the root of the database. Searching inboxes or all databases creates a global smart group, shown in the Smart Groups section of theNavigate sidebar.
On the left side of the main window, just below the toolbar, is the Path Bar. This is a specialized bar displaying a crumb trail to the current location in the Navigate sidebar. For example, if you are in a nested group, it will show something like Coding > AppleScript > WWDC > 416, always beginning with the current database.
Each item in the crumb trail is a live link, so you can click it to jump to any parent group or back to the top level of the database. Long-press a group to show its sibling groups. Or open the context menu via a Control-click an item to access them but also an Open button to open the group in a new main window or Reveal to open a new window with the group selected.
This bar also has < and > buttons so you can navigate back and forth between locations you've visited in this window. Bear in mind, these buttons only relate to the history of the specific window. If you open a new window, it will have no history so the buttons will not function until you've navigated to some locations. As an added feature, click and hold one of these buttons to be shown a list of previous locations you've visited, just like in a web browser.
Another specialized bar, the Information Bar displays the number of items selected and the total number of items in the current location. As mentioned previously, this bar also hosts the Sort dropdown and the view icons.