Just hitting the PrtScn key on my system will copy copy a screen shot to the clipboard.

It is best to then paste into the Paint program with windows and crop the the image to the area you want to actually use. This is how most screen shots are done.

If you want to get fancy their are professional screen shot programs that let you hit a hot-key then actually draw a box on the screen to choose what to capture, or click a window and automatically capture the contents of it.