Cutting out of any portion of an image is known as cropping.
Any part of the image can be selected by cropping.
A preview of the cropped image is visible at the right side.
The process to crop is:
1) Select the part of the image.
2) Select the shape of cropping tool from the menu.
3) Hold shift key and drag to select the marquee to a square or a circle.
4) Hold a marquee from its center, hold down Alt after dragging.
5) Select Image-> Crop menu item.