What do you want to cut? A whole image or a part of the image. You can use crop tool to cut the part of the image as per your requirement. Shortcut to cut the whole image is ctrl+x.
First of all you need to select the area which you need to cut. You can use various tools for that. Such as rectangular marquee/lasso/polygonal lesso tool/magic lasso and pen tool. After finishing your selection just ctrl+x, or edit > cut