This dialog box lets you define 32 horizontal and 32 vertical Guidelines. Guidelines act as a straight-edge, allowing you to align and place objects precisely. When an edge or center of an object gets close to a guide, that edge or center automatically snaps to the guide.
Direction
The direction of the guideline (horizontal or vertical).
Display Guidelines
Displays the guidelines on screen.
Snap to Guidelines (F7)
Activates the guidelines. When the guidelines are active, any object or group of objects that you create, move, or re-size snaps to the nearest guideline.