Do one of the following:
Share the whole screen: Click Share Entire Screen.
Share a window: Move the pointer to the window you want to share, then click Share This Window.
Share all windows for an app: Move the pointer to the window you want to share, then click Share All [App] Windows.
Tip: You can also start sharing from an app window. Click and hold , then click Replace [participant] Share with this Window.
Click in the menu bar, then click the Stop Sharing button. Ending a FaceTime call also ends screen sharing.