How do I redeem funds on my Apple id

Are you saying that you added money into your checking or debit card, and now you want to put a balance onto your Apple ID for iTunes or the App store?

If that is what you are asking you will need to buy an iTunes Gift Card and then you can redeem that card and apply the balance on that card to your iTunes/App Store balance:

Redeem App Store & iTunes Gift Cards and content codes - Apple Support

When/where are you being asked for a gift card code, what are you seeing when ? You will only be asked for a code if you are redeeming a card.