You are posting from online Premier but you are asking about the "download." Those are not the same thing. The online software is web-based---and you get ONE return per fee. The CD/download must be installed to your own hard drive on a full PC or Mac.
ONLINE vs. DESKTOP
When you use Online TurboTax, you get one return per fee. Each return needs its own account and user ID. If you use the same account and user ID for a second return, you overwrite the first one and lose it forever.
When you use Desktop TurboTax, which you install from a CD or download to your own hard drive, you can prepare and e-file multiple returns for the cost of the software. You can e-file up to 5 Federal returns—more if you mail the additional ones. If you have multiple returns to prepare for family members, Desktop is more cost effective.
Desktop --unless you specifically buy federal Deluxe only from a retailer-- will include the software for one specific state. You can prepare as many returns for that state as the number of federal returns you prepare. E-filing state returns is an extra fee which can be avoided by printing and mailing the states. Additional--other--state software is an additional fee for the software.
Looks like you are using TurboTax Online. In TurboTax Online, each tax return you prepare requires a separate account with a separate username and password, however, you can use the same email address for all of them. Be careful not to start another return by going back and overwriting everything in the return you just filed. This will replace your information and you won't be able to retrieve your tax return later.
For more information, please see the below TurboTax FAQ: