If you are expecting a federal refund you may have the opportunity to apply for the Refund Advance when you select your refund method. If you do have the opportunity to apply, you will be able to select Refund Advance in the Your refund info step of the File section. You must completely fill out your tax return, including entering your tax forms(such as a W2 or a 1099), before you can apply for Refund Advance.
If you have already filed your taxes, you cannot apply for Refund Advance. Please see the TurboTax FAQ About the Refund Advance application process for additional information.