Guides are horizontal or vertical lines you position to overlay your image. With the rulers displayed, you drag guides onto your image to help with precision work, such as cropping, moving image elements, selections, as well as text and brushstroke placement.
To place a horizontal or vertical guide you must be working in the Edit workspace.
If the rulers are not displayed, click View > Rulers. Then click View > Guides.
To place a horizontal guide, click the top ruler and drag a guide into position.
To place a vertical guide, click the left ruler and drag a guide into position. As you drag, the Status bar displays the guide’s position (in pixels).
If you double-click on a guide handle, the Guide Properties dialog box appears. Here you can change the position of the guide, change the line color or delete the guide.