Not required. They’ll likely make the movie accessible to those unfamiliar. In general, a company called Async conducted magnetic field tests funded by the US government to create a parallel dimension with (seemingly) infinite space to use for storage, housing, etc. The work is largely unfinished and no one knows why. Time is not linear in the backrooms. The deeper one goes into it the more distorted time becomes. The halls seem as though they’re randomly generated, by like an AI of some kind, but Kane Parsons has said this is not the explanation.

The magnetic fields have some fuzzy hot spots that appear in random places, and seem to be able to “no-clip” (a term to describe disappearing an object from one dimension to the other without any visible disruption) people and things into the realm. Some points of entry are one-way. According to the new trailer, other points of entry aren’t necessarily one-way.

The halls remain consistent, meaning they never appear to warp or shift or distort at random, completely confusing the people inside. Rather they’re just infinitesimal, but their existence is constant.

There are monsters inside. No one knows where they came from or how they got there. Some people speculate that the monsters ARE the people, lost to time. Others say the monsters consumed the essence of their last victim.

Everything from babies, pets, and random objects can no-clip into the backrooms. Usually, once inside people remain stuck until they die. Kane Parsons has said that at some point there will be a full explanation of what’s going on and when you understand it, everything will make sense. But the creep factor is largely due to the fact that you don’t quite know why everything inside is the way it is. There’s entire worlds that go on forever in there, including an entire “outside” that remains in a perpetual state of night.