Any explainer on what "Sovereign citizens" are talking about?

I see a bunch of videos on Youtube where Sov Cits interact with the police or judge, and I hear them making common claims, but I don't know what they're talking about. I'm having a hard time finding an explainer on what their logic is (even if that logic is flawed). Like, why do they keep saying they're "the real living person" - it sounds like they see that as different from the "All caps entity" that appears on their court documents? And what's their stick about admiralty law and jurisdiction about? There's other examples, but I'm just looking for something that explains these concepts from their point of view.