Thread:Ylimegirl/@comment-25679053-20141210212909/@comment-9645954-20141211041536

That's actually really easy. Press Command-Shift-4, and your pointer should change appearance. When you click and drag, you can choose the selection of the screen you want to capture, and it will be finalized when you let go.

Alternatively, pressing Command-Shift-3 takes a picture of the whole screen at once.