Can't stop screen sharing on Android tablet.

I am a casual Zoom user (two to three meetings a month) and I am trying to get Zoom on my Android tablet (Samsung Galaxy Tab S9) to work with little success.

1) How do I stop sharing my screen?

2) I can't get the microphone to work and, unlike Zoom desktop, I cannot find audio settings.

3) Is there a tutorial for using Zoom on Android?

Thanks.

Bill