refer: http://helpx.adobe.com/en/photoshop/using/grid-guides.html

Do one of the following:

• 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, and slices.

1. If the rulers are not visible, choose View > Rulers. Note:For the most accurate readings, view the image at 100% magnification or use the Info panel.
2. Do one of the following to create a guide:
   • Choose View > New Guide. In the dialog box, select Horizontal or Vertical orientation, enter a position, and click OK.
   • Drag from the horizontal ruler to create a horizontal guide.
   • Drag from the vertical ruler to create a vertical guide.
3. (Optional) If you want to lock all guides, choose View > Lock Guides.

1. Select the Move tool , or hold down Ctrl (Windows) or Command (Mac OS) to activate the Move tool.
2. Position the pointer over the guide (the pointer turns into a double-headed arrow).
3. Move the guide in any of the following ways:
   • 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.

Do one of the following:

• To remove a single guide, drag the guide outside the image window.
• To remove all guides, choose View > Clear Guides.

1. Do one of the following:
   • (Windows) Choose Edit > Preferences > Guides, Grid, & Slices.
   • (Mac OS) Choose Photoshop > Preferences > Guides, Grid, & Slices.
2. For Color, choose a color for the guides, the grid, or both. If you choose Custom, click the color box, choose a color, and click OK.
3. For Style, choose a display option for guides or the grid, or both.
4. For Gridline Every, enter a value for the grid spacing.
   • For Subdivisions, enter a value by which to subdivide the grid.
   • If desired, change the units for this option. The Percent option creates a grid that divides the image into even sections. For example, choosing 25 for the Percent option creates an evenly divided 4‑by‑4 grid.
5. Click OK.