1. To apply paint onto some surface. I brought in a bunch of pieces of cardboard and scrap paper for the kids to paint on. It's really hard to paint on textured, bumpy walls like this one.

2. To use paint to create a particular, picture, pattern, or design on something. In this usage, a noun or pronoun can be used between "paint" and "on." Can you paint a big dinosaur on Timmy's wall? He loves dinosaurs. I'm going to paint a cool fire design on the side of my car.