You have to set at least 1 "Classroom Option" on every Course that you activate. Use a Classroom Option that you can and love using. Currently you can choose from the following: Zoom, FaceTime, macOS Screen Sharing, Google Meet, MS Teams, and StreamYard. When they book your Course, they can only select 1 Classroom Option from the ones you have chosen.
Our recommendation for "screen sharing" is Zoom. But note that you, the Teacher, must have a paid subscription with Zoom in order to teach 1-hour Sessions.

Good to know: Students can search Courses based on these Classroom Options.