When you join a Zoom meeting created by another user, such as your instructor, you are considered an attendee. Your instructor will be the host and have host controls which will allow them to mute all attendees, share their screen with a PowerPoint or video, etc.

As an attendee, you'll see a menu bar across the bottom of your screen that will look similar to the image below:

Zoom Menu Bar-1.PNG

Let's look at what each of these items will do:

Mute / Unmute - Mute/unmute your audio, but not the audio of other attendees
Video - Turn your video on or off
Settings - Configure your settings for items like audio or video including changing which camera or microphone you're using
Invite - If allowed by your instructor, you can invite other participants
Participants - See a list of all attendees/participants
Share Screen - If allowed by your instructor / meeting host, share your desktop with all other attendees
Chat - Send a message to a) all attendees (public chat that will become part of the video if it is being recorded or b) a specific attendee (private that will not become part of the video); this is a good way to ask your instructor a question during a lecture or demonstration without interrupting the lecture
Record - If allowed by your institution or instruction, record the meeting
Leave - Leave the meeting

This bar may 'disappear' during the Zoom meeting, but it is really just hidden to not interfere with the video. Hover over where the menu should appear at the bottom of the window and it will reappear.