If you earn over $400 you have to pay esitmated taxes. There are self employement taxes for social security and Medicare as well as income taxes. Just know that the IRS wants their money asap.
The IRS wedsite has a wealth of information for business owners - they want you to pay your taxes and provide the information to help you.
I suggest you start here: http://www.irs.gov/businesses/small/...115045,00.html
You can also hire an accounting firm to help you this year - then use that return and information to help you moving forward.
Your estimated taxes are based on past quarterly earnings. Thus, if you earn so much during the last quarter - that is what you use to estimate.
Plus, you can pay online - makes it easy