How to categorize and record transactions

Hi everyone, what we do is sell products on Amazon. We have a credit card we use to purchase the items and a bank account where our sale/income goes through and we also use it to transfer funds to make a credit card payment. Both bank accounts are connected to Quickbooks Online.

1. How should we record/categorize the purchases from our CC (e.g. we purchased from Walmart to sell on Amazon) as an inventory? We usually don't repeat the same product ever.
2. I understand that we can categorize as a transfer the payment for CC in our bank, but how do we categorize it on the CC?
3. How do we record/categorize the sale from Amazon that goes into the bank account?

I appreciate in Advance all the insights you can give. Thank you so much!