Is your Mac frozen? Read on for an easy way to unfreeze your Mac.
Either click on your Apple menu in the top left corner and choose Force Quit or press the command, option and escape (esc) keys on your keyboard at the same time. The Force Quit menu will pop up.
Choose the application that is not responding by clicking on it until it is highlighted. In this example, Notes is not responding. Then click on Force Quit.
This should close the frozen application and you can try to reopen it to use it again.