Yes, if you are using TurboTax Online you must create a new account to establish a separate login for each return if you're filing separately. However, you can create a new login up to five users tied to your same email address if you'd like. Also, you can only prepare and e-file one federal return and up to five state returns per User ID. (See image below).

If you are using TurboTax Desktop, first save what you're currently working on by clicking File > Save As. Then, to start a new tax file, click File > New Tax Return. If you plan to prepare many returns, with the CD/Download products found here, you can e-file five federal returns and up to three state returns. However, only one state is included in the price. You can purchase and prepare as many additional state returns as you want.

Here's a link to jump directly to Create a new account in TurboTax Online: https://myturbotax.intuit.com/sign-up/