I've never heard of this. A plate, using a brayer...? Kinda sounds like an image transfer of some kind. I'll have to Google it!
....okay, so the little 4 minute video I watched had someone placing drops of paint on a glass plate, then using a brayer to roll them out, mixing a bit to get a pretty background. Then several stencil designs were pressed in. Some of these stencils were also painted on directly and pressed into the background colors. Circles, flower shapes, etc.
After applying several layers, a light coating of some kind of white medium was painted on, and then - yep, plain white paper was laid on top. (I thought this would be the time to use the brayer, but apparently smoothing and pressing by hand works fine.) The paper was peeled off, and the design had transferred to the paper. The glass plate can be rinsed clean and used again.
I'm guessing you could then paint or draw on the paper, once dried, and create something further. Paper type, weight, etc. would have to be considered in advance.
Interesting technique, one of those things that can inspire your imagination.
So - you get to show us your results!

Sounds like it could be lots of fun.