Guides and the grid help you position images or elements precisely. Guides appear as nonprinting lines that float over the image. You can move and remove guides.You can also lock them so that you don’t move them by accident.
The grid is useful for laying out elements symmetrically. The grid appears by default as nonprinting lines but can also be displayed as dots.
Guides and grids behave in similar ways:
Selections, selection borders, and tools snap to a guide or the grid when dragged within 8 screen (not image) pixels. Guides also snap to the grid when moved. You can turn this feature on and off.
Guide spacing, along with guide and grid visibility and snapping, is specific to an image.
Grid spacing, along with guide and grid color and style, is the same for all images.
You can use Smart Guides to help align shapes, slices, and selections. They appear automatically when you draw a shape, or create a selection or slide. You can hide Smart Guides if you need to.
Choose View > Show > Grid.
Choose View > Show > Guides.
View > Show > Smart Guides.
Choose View > Extras. This command also shows or hides layer edges, selection edges, target paths, slices, and annotations.
Drag the guide to move it.
Change the guide from horizontal to vertical, or vice versa, by holding down Alt (Windows) or Option (Mac OS) as you click or drag the guide.
Align the guide with the ruler ticks by holding down Shift as you drag the guide. The guide snaps to the grid if the grid is visible and View > Snap To > Grid is selected.
To remove a single guide, drag the guide outside the image window.
To remove all guides, choose View > Clear Guides.