Take a picture of your screen
You can use Preview to take a picture of all or part of your screen.
Entire screen: Choose File > Take Screenshot > From Entire Screen.
Part of the screen: Choose File > Take Screenshot > From Selection. Move the pointer to a corner of the area you want to capture, drag across the area, then release the mouse button.
Single window: Choose File > Take Screenshot > From Window. Click the window you want to capture.
The picture opens in Preview, named “Untitled.” You can annotate it by clicking the Show Markup Toolbar button and using the tools in the Markup toolbar.