When you get an incoming call, you will see a bar at the top of your mobile device:
You can either "Accept" the call or "Decline" the call
Mute your mic:
To mute your mic, select the mute button:
Place the Call on Hold:
To place the call on hold, select the "..." and select "Put call on hold"
to start video, select the video icon:
Your video will show on the lower right hand corner (you will not be able to have a virtual background)