Did you ever get to do the linoleum cutting prints in high school? This is kind of like that except no carving or special tools are required! It's actually just a rectangular jelly on which you spread fluid acrylic paint. Then you put the paper over top and it transfers onto the paper.
Why don't you just paint directly onto the paper, you ask?
I don't know. But this way is fun too :3
It would be difficult to describe how to use one of these with words, but Roben-Marie has put together a fantastic video tutorial which answers all of the questions!
I used bubblewrap, string, circles of paper, a stamp, a regular paintbrush and some plastic canvas I had laying around.
I suppose you could paint it on with a brush, or perhaps they expected this to only be popular among experienced printmakers who already have the tools... In any case, I ran down to the Michaels with a coupon and bought the simplest brayer I could find.
People are coming up with some pretty cool ideas.