How do I paint patterns on garage floors?

How about with a stencil?

I can tell you from experience, you DO NOT want to paint a garage floor. concrete is not the most suitable surface for paint, will either peal or scratch off.

I would suggest you stain it and then seal it.

Karen, there are a number of ways listed on how to do this in DIY. If you click on "explore projects" and type in "paint garage floor" in the search box and hit enter, you will find them. I have chosen one for you, I hope it helps. https://www.hometalk.com/diy/floors-ceilings/how-to-paint-concrete-paving-34224326

Prepare & Paint Concrete | Garage Floor | Paving Paint

Love the link from DesertRose. There are garage floor paint kits you can buy.

I would use a stencil!

This looks nice: https://www.hometalk.com/diy/outdoor/garage/diy-garage-floor-tutorial-rocksolid-polycuramine-10429782

DIY Garage Floor Tutorial: RockSolid Polycuramine