Guides in Photoshop
Guides are horizontal or vertical lines that can be placed or positioned anywhere on the image surface. To change position of a guide line just drag the guide line to the new position.
How to create a Guide
How to delete a Guide:
Select the guide and drag it out of the image.
View -> lock Guides
You can change color and style of the guides from:
Edit -> Preferences -> Guides, Grids & Slica