If you have a C-corp, and it has US-source income, you need a tax professional, and you will likely spend most of that income on their services. Sorry.
If you have an LLC, the pain-minimizing steps is to fill out a personal tax return with a Schedule C-EZ attached to it. Write the revenue number on the schedule C-EZ. Normally you'd calculate expenses for the business and subtract them, but understating your expenses is not a crime, so save yourself the hassle and just write 0 for all of them. I'm assuming you're asking this question because you're not physically in the US and this company is your sole US-source income, so when you flow that number to the places the Schedule C and 1040-EZ tell you to put it, you'll find that you have 0 tax due. Sign return, mail in, keep copies of the return and documentation of that income number for 6 years.
If you don't want to have to read instructions, TaxAct is fairly decent SaaS for uncomplicated returns, and should be able to handle a simple LLC filing. I used it for rather substantially more complicated returns for 7 years prior to getting a real accountant. I think it will run you about $15.
Depending on where the company is incorporated and how it earns its income, you may have to file state income taxes. You may also have to pay state/local taxes or fees. If any of this is news to you, talk to an accountant.
Delaware has no corporate state income tax IIRC.
Edit: I skimmed over the last and most important line of Patio's reply so I figure so I should reiterate it and not seem completely contrary: You NEED to call an accountant.
(I'm almost certain that filing as an S-Corp is cheaper than as a C-Corp, but not as clear on the conversion cost, which might be trivial or might not.)
You need to talk to an accountant. Don't put this off. Being in the hole on taxes really, really sucks.
I'd consult an accountant.
That's one advantage of not incorporating until your revenue is greater than a certain amount. If your business is not incorporated, you can do a Schedule C yourself.
