How to make full screenshot?

It can be handy when you are in a  hurry and want to make a full screenshot.

Force close a program Mac Shortcut

To force close a program hit Option+Cmd+Escape,
This screen wil appear.

How to make screenshot with Mac

Hold down the key shift + cmd + 4.

Your mouse point will turn in a cross, just drag the mouse
while holding left mouse click. 
After not holding the left mouse click, it will make a screenshot of the area and it will automatically save to desktop.