how to use async for?

what does async for do? or, how do async iterators in general work, because I'm pretty sure async for just helps you iterate on an async iterator.

I think async iterators have a method __anext__() which "steps through the iterable"? I don't understand what stepping through means.

Also __anext__() returns an awaitable? what does that mean, especially if I have something like an AsyncIterator[Object], what does the awaitable have to do with the object?