How do I report business income

I don't envy you and the task you are about to undertake for the first time. IRS.gov might be the first place to start getting an understanding of what you need to do.

Who filed the 941's and all the rest in 2020? Did your client have a prior accountant? Unless you personally know the client, there are a lot of questions to ask to make sure you are performing sufficient CYA practices.

Thumbs up to the two prior replies... in my opinion you should have sufficient knowledge of an area before you undertake a task... If not, then you should obtain adequate knowledge as soon as possible via continuing education... I'm just trying to help you... Good luck .... Just my opinion...

I have to agree with everyone else: the basics of your questions mean this is already beyond your ability to do it on your own.

The terminology matters, so we already see a problem here.

This statement, for example: "and he makes his own salary."

No, that won't happen. He will either not have a "salary" or gets paid from his Corporation through payroll.

Where you might start is with a basic intake questionnaire. But, if you don't know what things are called, you won't understand them when you get the right info from a client, but even worse, you won't notice when you get bad info from clients or inadequate info. And you won't know what to ask about, to help get it right. Yet, you are sworn to be performing this profession as a legal responsibility.

I recommend that you get the training you are supposed to have, the continuing education each year (because things change) and find someone to work under who can mentor you.