How can I render a react-native view on an RCTSurface?

I'm really trying to figure out how RCTSurface works but I haven't found any good examples.

I want to be able to define a view from the javascript side of react-native, but then use it inside a native UIView that I control via native code.

(I know I just mentioned iOS names above, but this topic interests me for Android as well)

Can someone tell me how RCTSurface is supposed to be used?

Thank you