By default, moderators manually add webcam participants to the stage. This gives you the ability to control who goes on stage and when.
If you are running a class or a meeting, then auto-to-stage is a great way to get all participants on stage quickly and easily.
At the top of the participants list you have an option to control all participants:
Click corresponding to ALL so that all webcam participants currently in the session as well as those that join are automatically added to stage when they turn on their webcams & microphones:
When auto-to-stage is set then all webcam participants up to 25 are added to stage automatically. When a user is removed from stage or leaves the session, then the next available webcam participant is automatically added to the stage.