Business registration and taxes are the top two things for selling. If you are not selling, skip right past unless you might want to sell in the future (then, of course, stick around!).
Business Registration: This is letting your city/county/state know you exist. This is also letting the state know you exist AND are selling something that they place a tax on.
Taxes: This is the money owed to the state and/or to the federal government. There are lots of types of taxes so the next lessons will hopefully give you enough information to know what you are looking at and when.
Sorry, Charlie, but there isn't actually any threshold where you don't have to worry about this. The federal government (IRS) wants to know every penny that comes in. You may have seen this "threshold" of reporting from others at $400, well, the thing here is that there are two places where you can report the income and the $400 is the point when you have to fill out a new form. Confusing? I know, I'll clear this up in the next lessons. For now, just know that this myth is a misunderstanding and not a real thing.