Your whole screen
- command (⌘) + shift + 3 Key
 
Just a window
- command (⌘) + shift + 4 Key
 - Press the space bar.
 - Choose any window and then just click your mouse or trackpad.
 
Just a menu (Right click menu)
- Show the menu
 - command (⌘) + shift + 4 Key
 - Press the space bar.
 - Choose the menu and then just click your mouse or trackpad.
 
Part of your screen
- command (⌘) + shift + 4 Key
 - Just drag to select an area.