Once you click on the link from a Facebook page this is first screen you see. Select launch meeting
This is the next screen. Select Open app. Facebook is just letting you know that you are leaving them.
Lastly this is to enter zoom meeting page. It says to hear other please join. Select Wi-Fi or cellular data.
At the bottom left you can choose to mute and unmute yourself and you can either share or unshare your video. If your screen looks like this nobody can hear or see you but you can watch and hear those that are sharing their sound and video
The last thing is the leave button. It is at the top right of the screen. Push this button when you want to exit the screen.
If you want to practice the link is always active. You can sign on and off prior to the meeting and get comfortable with the functions of this screen.