To teem with things is to have lots and lots of them. In other words, when a place is teeming with things, it's very full of them, and they're all moving around in a busy or active way.
This room is teeming with raccoons! That means it's overflowing with raccoons, all moving around.
Usually, when a place teems with things, those things are moving around busily, like a cafeteria teeming with children, or a fish tank teeming with fish.
But we can say that a place is teeming with things even if they aren't really moving. For example, Belle's library is teeming with books.