How can I find out what I am being charged for and manage my apple pay account?

When you say Apple Pay account, do you mean Apple Cash account? There is no such thing as an Apple Pay account.

The support article I linked to below explains how to manage your Apple Cash account and how you can view/download your transactions.

>> View your balance and transactions

Tap the Apple Cash card to view your balance and latest transactions. Scroll down to see your transactions grouped by year.

You can also do the following:

• Search your transactions: Tap , enter what you’re looking for, then tap Search on the keyboard. You can also choose a suggested search, such as a category, merchant, location, or contact, then enter additional text to refine your search.
• Get a statement: Tap , tap Card Details, scroll down, then tap Request Transaction Statement. <<

Set up and use Apple Cash on iPhone (U.S. only) - Apple Support