In case you are new to Mac or just forgot the holy key for screen printing.
No panic. Here’s the recipes!
1) Full screen capture
For full print screen, press ⌘ (Command) + Shift + 3. The screen captured will be saved to your desktop.
2) Partial screen capture
If you wish for screen capture a partial of the screen, press ⌘ (Command) + Shift + 4 and drag to select the area you want to screen capture.
3) Application screen capture
And if you have a needs to screen capture for an application, press ⌘ (Command) + Shift + 4 and press spacebar. It will allow you to choose the app that you wish to screen capture.
All image captured will saved to desktop prefix with “Picture”.
source : dottony.com