Hi Jacob_Phillips,
Welcome to the Apple Community, where some of us do our best to help each other :)
Wondering if you were logged in to the App Store with your Apple ID ?
Your Apple ID is the account to use for adding a payment method to use for everything Apple.
including iTunes, App Store, iCloud, subscriptions etc.
It seems Apple require you to have a payment method in your Apple ID for the first time you use iTunes and the App Store, even if you are downloading a free (Get) App.
The links below are to Apple Support articles, that can guide you, if you wish.
First: Check the payment methods that you can use with your Apple ID:
(Scroll down to see the various countries listed)
https://support.apple.com/en-us/HT202631
Then:
How to create your Apple ID if you do not have one::
https://support.apple.com/en-au/HT204316/
OR
if you do have an Apple ID account :
Apple ID Log-in:
https://appleid.apple.com
Now you can:
Change, Add or Remove Apple ID Payment methods
https://support.apple.com/en-us/HT201266
After you have used your Apple ID in the App Store and iTunes for the first time,
seems it is possible to remove the payment method, if you wish:
How to remove payment methods from your Apple ID.
https://support.apple.com/en-us/HT204034
or
If you can't remove your last payment method or use no payment method with your Apple ID
https://support.apple.com/en-au/HT203905
Hope this helps you :)