Breakout Rooms allow you to put participants into 50 different rooms so that they can work in a small group. The host moves back and forth between the rooms engaging participants in discussion.
Enabling Breakout Rooms takes place in Settings. This has to be done before trying to get Breakout Rooms to work. The link above goes step-by-step to enable this feature in Zoom.
Zoom provides an excellent tutorial on how to run a Breakout Room.