ELI5: How does starting a business work in the US?

I’ve tried to learn how to start my own business, but I keep hitting a wall in terms of what paperwork, rules, and other things are required.

I go in looking for essentially a check list of what I need to get started and keep it running for the first couple years. But then I get slammed with so much info I can’t tell what’s helpful and what isn’t.

People I’ve asked keep talking about LLCs but I have no idea how to get one, use it, or what it’s actually for or if it’s even necessary.

Any help is appreciated. Thank you.