The multiverse operates around three basic principles. Learn these, and a basher'll have a head start on understanding how things really work.
The Center of the Multiverse: Primes think their little world sit at the center of it all, but it ain't true. Fact is, nothing sits at the center of the multiverse - how can there be a "center" of an infinite expanse? So, really, no place is more important than anywhere else. By the same token, wherever a body stands is the center of the multiverse – at least from his perspective.
The Unity of Rings: The multiverse tends to form endless rings – whether physical or philosophical. Sigil, the Outlands, the Outer Planes, and even the Elemental Planes form rings without beginning or end. Follow any ring, and a body'll always end up where he started.
Rule of Threes: Things happen in threes. Simple enough? It's not logical, but it's almost always true.