For this you must do the following. Move your mouse to the top left point of the are you want to capture and press your primary mouse button. Drag the mouse to the lower right point of the screen that you want to capture. Notice that a rectangle is being displayed that highlights the area of the screen to be captured. You may use arrow keys for define of a precize size of the area.
Clip copy the image of select area to clipboard.
Defrost defrost the screen. If you will not select area, you will work with full screen area. You can set hot keys independently. This program is shareware.