This video demonstrate how easy it is to take screen shot with shortcuts in Mac OS X. Press Command+Shift+4 will make the cursor change to cross-hair, indicating it is ready to take screen shot. You can then draw on screen where you wish to take a shot of. By default a new image will be saved on your desktop. Open the image by double-clicking it and click on File, Save As to save the image as your desired format (JPEG. JIFF, etc.) and with preferred size. When taking window screen shot, use same shortcut then press the space bar. This will take snapshot of the active window. Follow the same steps to save the image as JPEG or other formats.