React Components are the easiest way to build real-time audio/video apps with React. No need to manage state or events; it's all done for you.
Prefabs use components under the hood and add additional features, styles, but also reasonable defaults. They are designed to be opinionated and not meant to be extended. You can, we just don't build them with that in mind.
Layouts are components that help you arrange participants in standard video conference layouts.