To file an additional return using TurboTax Online, you will need to create a new account. Please see the following TurboTax FAQ for instructions on how to start another return using TurboTax Online. If you have several returns to file, you may be interested in purchasing a TurboTax CD/Download, as you can e-file up 5 federal returns for no extra charge, whereas you will be charged for each return (unless eligible for free filing) using TurboTax Online.
If you are filing another return to report other tax documents for yourself, be aware that you file all of your W-2 and other tax documents on one return for each tax year. If you need to add anything to your return, you will need to amend your original return to include anything that wasn't on the original return.