Your taxes are one of the key items you'll need in order to fill out the FAFSA®.
If you (or your parents) used an online tax filing service like TurboTax, they'll be able to log in to that service and get a copy of it.
If you (or your parents) used an accountant to file taxes, your accountant will be able to provide a copy of your tax return, including all the forms.
Otherwise, you can get an official copy straight from the government here. Click the "Get Transcript Online" button and follow the instructions. If asked for what type of transcript you're looking for, choose Tax Return Transcript. Note that to do this, you'll need to have access to the following information:
your SSN, date of birth, filing status and mailing address from latest tax return,
access to your email account,
your personal account number from a credit card, mortgage, home equity loan, home equity line of credit or car loan, and
a mobile phone linked to your name (for faster registration) or ability to receive an activation code by mail