There are several useful keyboard shortcuts for taking screenshots on a Mac.
Command + Shift + 3 – takes a screenshot of the entire screen and saves it as a file on your desktop.
Command + Shift + 4 – turns the cursor into crosshairs, with which you can select an area of the screen to capture. Captured image is saved as a file on your desktop.
Command + Shift + 4 and then press Space – turns the cursor into camera icon, with which you can select to take an image of the current window, the menu bar or the Dock. Captured image is saved as a file on your desktop.
If you want to save the captured image to the clipboard instead of directly to a file on your desktop, add Control key to the combination. So you would press Command + Control + Shift + 3 and Command + Control + Shift + 4.
Another way of taking screenshots is to use built in Grab application. It allows you to capture section of the screen, specific window or an entire screen. It also has a timer functionality, which captures the screen ten seconds after the timer has been started.