How can users be divided into groups during a Zoom meeting?

In Zoom, there is a "Breakout Session" option that allows users to be split into smaller rooms in a Zoom meeting.

The assignment of users to rooms can either be done manually or automatically. In case of an automatic assignment, it is possible to define the number of participants and sessions.
Furthermore, participants can be allowed to return to the main session from their breakout session or, if necessary, forbidden to do so.