PDF (adobe.com)

Guides and Grids preferences

Color boxes
When clicked, display a pop-window from which you can select a color or enter hexadecimal values.

Show
Displays guides or grids on the canvas.

Snap
Snaps objects to guide or grid lines.

Lock
Locks previously placed guides in place, preventing you from inadvertently moving them while editing objects.

Snap Distance
Specifies how close the object you are moving must be (1 - 10 pixels) before it snaps to a grid or guide line. Snap Distance works when Snap To Grid or Snap To Guides is selected.

Grid Settings
Change the size, in pixels, of grid cells. Enter values in the horizontal and vertical spacing boxes.