To share another computer’s screen:
Go to Finder, and open any folder. In the sidebar of a Finder window, look in the Shared section for the shared computers on your network. (Click the disclosure triangle next to Shared if it’s not expanded.)
Select the computer whose screen you want to share, and then click Share Screen in the main part of the window.
Select how you want to connect to the computer:
As a registered user:
Select this to connect to the other computer using a valid login name and password. If “Only these users” is selected on the other computer, make sure the login name you’re using is on the list of allowed users.
By asking permission:
Select this if you want to ask the current user of the other computer for permission to share their screen.
To set up screen sharing:
Choose Apple menu > System Preferences and click Sharing.
Select the Screen Sharing checkbox.
To specify who can share your screen, select one of the following:
Select this if you want to allow any user with a user account on your computer to share your screen.
Only these users:
Select this if you want to restrict screen sharing to specific users.