This isn't directed at anyone in particular, but a while ago I summed up the lore of King's universe for someone, and it might be helpful or relevant to some people here:
There was first a primordial chaos filled with an infinite number of insectoid dark magical demons.
This place was called "Prim".
The two most powerful entities, a "man" called Gan and his wife called Bessa created the known universe from this darkness. Gan's body became the multiverse itself, a giant tower that was both at the center of, and all of creation, with each floor of the tower being a different world/universe. The old primordial darkness surrounding the tower became known as the "Todash darkness", or the dark formless void that lies in-between and outside of creation.
At some point, a very early civilization progressed technology to the point of basically being magic, a mega-corporation called North Central Positronics replaced the magic pillars holding up the Dark Tower with mechanical versions and created giant magi-mechanical cyborg animals to guard them (One of these is The Turtle from IT), along with a slew of other plot relevant magi-tech.
A short time after that, one of these Todash/Prim creatures mated with a human (King Arthur Eld) on a world called Mid World, they had a half human, half demon son who grew up to be a powerful ruler named The Crimson King, and he made it his mission to destroy the six beams of the Dark Tower and crumble existence back into the formless chaos of Prim. (Yes this is very Arthurian)
So an ancient line of "Gunslingers", an order of knights who's duty as to keep reality from collapsing was formed, and their last surviving member a man named Roland Deschain goes on a quest to stop The Crimson King from succeeding. That's the basic plot of The Dark Tower, and by the nature of that series, also the plot of King's entire universe.
Also relevant:
Sometimes humans are born with psychic powers, that's a common theme too, it's called "The Shining" or "The Touch" but it's all the same, from the same place. The kids from Firestarter, and from Dreamcatcher, Rose Madder, and of course from The Shining all had variations of the same power.
Sometimes the primordial creatures from this void make it through into the tower, there have been a lot, from the insectoid creatures that invaded Earth during the rip into the todash with "Project Arrowhead" (The Mist), or the giant psychic spider creature that terrorized the small town of Dairy, Maine (IT), or that same species of creature that appeared in the Dark Tower named "Dandelo", the giant Ray (The Shining) pretty much every single monster, demon, god, or entity from King's books is actually one of these demons from this void.
*Note there may be some inaccuracies, plot holes, or minor inconsistencies smoothed over for the sake of coherent lore summary.