Activate and bring stickies to the front by (double-)clicking on them.
Move stickies around by clicking on and dragging them. The optional grid, see Preferences, simplifies positioning. Hold Shift to disable snapping to the grid.
Rotate stickies to the left/right by 10 degrees or use the Inspector to set any desired rotation. You can enter a radian angle or use the circular slider to rotate images in realtime. Hold the Shift key to snap the angle to the markers.