While in a facetime call, hit the three dots (…) and there is an option for share screen, you can either share yours, or request the other person to share theirshow do i do that?
During screen sharing, you can touch the screen and it makes an effect the other person can see so you can circle things, etc to point them out. Or you can request to control their screen as well. Another nice thing is that sensitive information like credit card numbers and such are automatically hidden during screen sharing