You don't file a tax return every quarter. You just make quarterly payments of estimated tax. You file one tax return at the end of the year. The estimated tax payments that you make during the year are applied towards the total tax for the year on your tax return.
You can make estimated tax payments online using Direct Pay on the IRS web site. Make sure you select the correct year. If you want to make estimated tax payments by mailing a check, use Form 1040-ES for the applicable year.
For details about estimated tax, see Chapter 2 of IRS Publication 505.
