The ending was very confusing to me as well until I watched part of the original YouTube playlist. The original content is 22 videos long. That's a lot of footage; one of the videos is even 45 min long. Backrooms is really ultimately an extended sequel to all of that content, so I would strongly recommend that you watch at least the first 5-10 videos of Kane's original playlist on YouTube. He even has an official one in order, so that makes it easy to go through.