Are you sharing a video for class but the audio isn't coming through for attendees?
Zoom Support provides the following instructions on how to access the Share Sound button in the share selection window.
"Zoom screen sharing allows you to share the desktop, window, application, or audio/video. If audio is an important part of your shared content, you can also send the computer's audio (in mono or stereo) to the remote attendees when sharing, providing a more professional and immersive sharing experience."