If you are using the TurboTax desktop CD/Download editions installed on a personal computer, then click on the File menu at the top left of the desktop program screen. Then click on New Tax Return
If you are using the TurboTax online web-based editions then you can only complete and file one tax return per account. If you need to complete another tax return then you will need to create a new account with a new UserID. You can use the same email address for up to 5 online accounts.