I am not an accountant and this is not "professional advice."

I do have an S-Corp, though.

You need a corporate accountant. A public accountant cannot do corporate taxes.

You pay by the March 15 deadline like everyone else. UNLESS you are earning more than a certain amount a year, which your account can advise you of--then you will likely pay quarterly remittance which is an estimate based on revenue and then adjusted at fiscal year-end. If you're earning under say $200K, don't worry about it: you're still on the standard tax plan.