This would apply if you were living in one state and working in another. You would be filing both a resident state tax return for the state you live in and a nonresident state tax return you earned money in.
When you create a Resident state return and a Non-Resident state return, TurboTax will calculate the credit for taxes paid to another state, if applicable. This is so you are not double-taxed on your income.
In general, you pay the tax in the state you worked in and your resident tax return gives you a credit for it. It can be found in the "Additions & Subtractions" section of your state tax return. It would depend on what states are involved (how the additions/subtractions would work).
Click here for information regarding filing multiple state returns.
Click here for additional information on filing when multiple states are involved.