Zoom has created these tutorials for using breakout rooms:

• Managing Breakout Rooms  - gives a overview of how to set up and run this feature, as well as providing a short video demonstration and a discussion of limitations.
• Pre-assigning participants to Breakout Rooms - shows an alternative to assigning participants after the meeting has started; instead, pre-assign them for the meeting by logging into your account on the Web. This article provides an example .csv file you can upload with your students names.
• Participating in Breakout Rooms - gives an overview of the steps to participate in breakout rooms on different platforms (Windows/Mac/Linux/Web) and devices (Android/iOS/telephone)

Many institutions have created articles on how breakout rooms can be used with a class in Zoom to facilitate interactivity and group work. In particular, I like this one from University of Colorado Boulder's Center for Teaching and Learning:

• Facilitate group work - In particular, check out the section "Keep students on track" for specific ideas for successfully integrating the rooms into your instructional plan. Also, be sure to watch their short video on using a Google Doc to structure students' group activity (linked within the page)