Using guides in Photoshop

After the guides are in place, here are a few of the things you can do with them:

-->Turn the Snap to Guides feature on or off: Choose View➪Snap To➪Guides.

-->Lock all guides so you don’t accidentally move them: Choose View➪Lock Guides.
You can also select Alt+Ctrl+semicolon (Option+Ô+semicolon on the Mac).

-->Remove all guides and start from scratch: Choose View➪Clear Guides.

-->Change a horizontal guide to a vertical guide (or vice versa): Hold down the Alt key (Option key on the Mac) as you drag the guide.

-->Align a guide at a precise location on the ruler: Hold down the Shift key as you drag a guide to force it to snap to the ruler ticks.

-->Create a new guide in a precise location: Choose View➪New Guide, click the Horizontal or Vertical option, and type in a distance from the ruler where you want the new guide to reside.