Hi kanisha163,
welcome to the Apple (user-to-user) Community.
Re: I’m not even sure what I need to be paying for
How to see what you were charged for:
If you see "apple.com/bill" on your billing statement – Apple Support
Re: My card keeps declining when trying to add payment method and download apps
You might need to check that your payment method is one that Apple can accept in your country or region:
Payment methods that you can use with your Apple ID – Apple Support
Why does Apple keep declining my payment method when the funds are there:
What to do: If your payment method has been declined in the App Store or iTunes Store – Apple Support
Eg: says:
"You may need to ask your financial institution to allow international purchases on your debit or credit card". (Seems it is not Apple that declines ...)
“If you've disputed a charge from the App Store or iTunes Store, you might need to contact your financial institution again to authorise that charge and future purchases from the App Store or iTunes Store”.
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Re: "the funds are there".
Eg: if the funds are from adding gift cards
What you can buy with your Apple Gift Card or Apple Account balance – Apple Support
Eg says:
"Some purchases might require that you have a credit card on file, even if you use your Apple Account balance to make the purchase."
and
"Some stores and apps might not be available in your country or region.
Find out what's available in your country or region."
All the best :-)