While you need to educate yourself on the self-employment aspect of taxes, here's a quick answer to your question.
First, you do not "FILE* a quarterly tax return. You *PAY* quarterly taxes. If your state taxes personal income then in addition to paying quarterly taxes to the IRS, you must also pay quarterly taxes to your state.
Now the IRS provides all these worksheets for figuring your quarterly taxes. But having been self-employed for over 15 years now I can tell you that it's an absolute waste of time, resource, and brain power. If you elect to use the worksheets, your quarterly taxes due will come out somewhere between 19% and 23% of your *GROSS* business income. So if you just send the IRS 20% of your *GROSS* business income each quarter, then come tax filing time you'll be fine. You can pay your quarterly taxes to the IRS online at www.irs.gov/payments. *PRINT* *YOUR* *RECEIPT*!!!!!
If your state also taxes personal income, then you will need to pay your state quarterly taxes separately. How you do that, depends on the state. Not all states offer the ability to pay quarterly taxes online. So you should check the website of your state's taxing authority. When you pay your state, if you pay an amount equal to whatever rate your state taxes personal income at, then you'll be fine at tax filing time. For example, California has the highest state taxes at 13%.
