Yah, retro uses post-its.
Retiform is when you sponge to create lines that create odd shaped blocks to stamp in.
Retro, you mostly cover your GLOSSY paper with post its. You should have a few colors picked out to brayer. First brayer your darkest color over the post its and paper. Then remove a few post its, brayer your next color, remove more post its, brayer lightest color. Some people leave some white showing too. You can stamp right on it or layer on it.