In a Teams meeting a lecturer might share their screen. This way, a lecturer can show students a presentation, a document or a part of a website. Depending on the settings configured by the lecturer (the organiser), you can also share your screen as a participant.
Viewing the screen of someone else
If someone in the meeting shares their screen, this will appear large on your screen and all other participants will appear small.
There are differences in view and possibilities in the browser and the desktop app.
The organiser can set that students can also share their screen.
More information about screensharing can be found here.
A lecturer can also use a whiteboard during a Teams meeting.
More information about the use of a whiteboard can be found here.