SHIFT+CMD+3to take a screenshot of the visible window
SHIFT+CMD+4to capture a portion of the screen using a crosshair selection tool
SHIFT+CMD+4+SPACEBARto capture a window or menu. This adds a nice shadow below the window.
For more info see take a screenshot with your mac.
Written by Jaime González García , dad, husband, software engineer, ux designer, amateur pixel artist, tinkerer and master of the arcane arts. You can also find him on Twitter jabbering about random stuff.