Here are the steps to screen share on a Mac:

1. On the Mac you want to share, choose Apple menu > System Settings, click General in the sidebar, then click Sharing on the right. (You may need to scroll down.)
2. Turn on Screen Sharing, then click the Info button on the right.
3. Note the name and address of the Mac (it’s listed at the top), then click Done.
4. To share your screen on a Mac locally, go to System Preferences > Sharing.
5. Click Screen Sharing and choose All Users.
6. On another Mac, click Go > Connect to Server and paste the VNC address.
7. Enter your username and password.

I hope that helps! Let me know if you have any other questions.