I have used embossing folders as stamps before. I used the Sizzix gear folder as a stamp on a background. I just used my ink pad to ink the embossing folder though because using a brayer takes more time, but the brayer might get better results. I put the paper I was stamping onto my big stamp pad which is just a big piece of craft foam to stamp so it would pick up more of the image.
I have also inked the inside of the folder, closed it over the paper, and run it through my Fiskars Fuse. So I have used them several different ways. You can also put acrylic paint inside the folder the same way you would ink. I have used the dobbers paint to apply the paint inside the embossing folder. That turned out really well too.