Breakout rooms are now available to use since the latest update - this feature allows you to create separate rooms within your meeting and to assign participants, for example, to discuss topics in smaller teams.
Only the organizer can start a breakout room from within the Teams desktop app. Participants can join and use the breakout rooms from desktop, web, or mobile.
To use the new feature, you should make sure that the new meeting experience is enabled (Teams -> Settings -> General -> Check “Turn on new meeting experience”).
The organizer can create a new breakout room by pressing the new Button (Directly to the right of the "Raise hand"-Symbol) and choose to allow it to be filled automatically or assign participants manually. In the room settings, you can also configure if you want to allow participants to return to the main meeting by themselves or if you want to do this manually.
Further information can be found here: