If you are going to use the TurboTax online editions then you will need to create a new account and User ID for him to complete his tax return - https://turbotax.intuit.com/personal-taxes/online/
If you are going to use the TurboTax desktop CD/Download editions then all you need to do is start a new tax return for him. Click on File in the upper left of the desktop program screen. Then click on New Tax Return.
https://turbotax.intuit.com/personal-taxes/cd-download/
