Crop Tool

• In the Toolbox, select the Crop Tool, click on the image and draw a rectangle holding mouse's button pressed.
• When you release the button a bounding box appears. You can move, resize and rotate it. To move bounding box by a few pixels you can use keyboard cursor keys.
• While bounding box is active you can choose Hide or Delete option: Delete completely remove cut-off (shielded) parts of the image; Hide only hides them, so you can make them visible later on using Move Tool..
• To apply crop you have either to press [Enter] key or right-click on the image and choose command Crop in context menu.
• To pre-define target image size fill Width, Height and Resolution fields on the Options bar. Units (cm or inch) have to be specified in the same fields; otherwise Photoshop sets it to px (pixels).
• Note that while bounding box is active the rest of Photoshop tools and commands are not available. You have either to apply [Enter] or to discard [Esc] crop to resume the work.

Tip. Just in case you didn't know, the Crop tool is also available in Photoshop Elements that is way cheaper version.

And if you believe, Photoshop Elements lacks some other important feature, be sure to visit this page.