General Business Stuff Help

This is not related to electric skateboarding but the business part. First off, I’m in Los Angeles, California. Second I’m trying to sell a bunch of used books I have under the hobby designation for business purposes. I’m trying to figure out which specific form I have to fill out and who to go to so the tax man can’t one up me. I’m asking on this forum because I know there are a few users here who have set up shop in California.