[spoiler]It’s about alternate universes, man. Oh, and time travel.
Seriously. That’s pretty much what I got out of the the most recent episode. There are a bunch of people from different times and possibly different dimensions wandering around a spot in the Derry woods (I think this has something to do with the Dark Tower’s beams) and the grown up Henry in the cage in the first Derry we’ve been shown is from now-Derry-2, while little boy Henry from then-Derry-1 was held captive by Derry-2’s version of his dad, but now, instead of then, so he moved through both time and dimension.
What any of this has to do with why the town is “bad” or 2/3rds of the things unrelated to the Henrys and Mollys, I still don’t know. [/spoiler]