Use hot corners on Mac
You can use the corners of the screen as hot corners, to quickly start actions when you move the pointer to a corner. For example, you can start the screen saver when you move the pointer to the top-left corner of the screen, or lock the screen when you move the pointer to the top-right corner.
Tip: By default, the bottom-right hot corner is set to Quick Note, so you can quickly open a note to jot down your thoughts at any time. See Create or edit a Quick Note.
On your Mac, choose Apple menu > System Preferences, then do one of the following:
Click Hot Corners.
For each corner you want to use, click the pop-up menu, then choose an option, such as Notification Center, Launchpad, or Lock Screen.
To use one or more modifier keys with the hot corner, press and hold the Command, Shift, Option, or Control key while viewing the pop-up menu.
When you’re done, click OK.
When you move the pointer to the selected corner of the screen (and use a modifier key, if you set one), the selected action starts. To stop the action, press any key, move the mouse, or touch the trackpad.