It depends. Arizona Form 309 figures out your credit for taxes paid to Arizona and another state on the same income. Usually, if you have sourced income from a nonresident state and pay tax to that state, your resident state will give you a credit of taxes paid so you are not double taxed on the same income.
If this does not describe your situation, then you can skip over these questions. If you do have double sourced income, please input the amount of income that was subject to tax by your nonresident state.