Want to work in the US for a year, not sure what I need

So I want to stay in the US for a year, and I want to be able to work while doing so. Couple questions regarding this.

1. Do I need a regular visa and a work visa?
2. Can I get a work visa once I'm already there?
3. Will a work visa last for a year or does it also need renewing like a regular one?

Any help would be super appreciated, as well as any information you might consider useful!