Greeting, Picasso.
Welcome to the Community. I'd like to provide some insight on your questions about posting payments in your parent and sub-accounts, as well as reconciling.
If each card is a sub-account under the one central billing account, some users have posted payments under the sub-accounts. I recommend speaking with your accountant about this to make sure what would be best for your business setup. Additionally, this article explains using credit card sub-accounts in QBO: https://quickbooks.intuit.com/community/Banking-and-bank-feeds/About-bank-or-credit-card-sub-account....
The idea of reconciling can sometimes be intimidating, but I've got the resources for you that will help. Reconciling is matching your actual bank statement to transactions in QuickBooks. Grab your paper statement and a cup of coffee and you're ready to get started. Here's how:
1. Click the Banking tab in the left navigation menu.
2. Make sure the account you'd like to start working in is highlighted blue at the top of the page.
3. Select the blue Go to Register link on the right side of the page.
4. Click the green button labeled Reconcile.
5. Starting with the oldest statement you have that hasn't been reconciled, enter the Ending balance and Ending date exactly as it appears on the paper.
6. Choose Start reconciling.
7. You can click the very top circle to select all transactions and then look for any differences, or you can start checking them off one-by-one as the appear on the statement.
8. Once you hit the goal of having a $0.00 difference, you're ready to move on to the statement for the next month. Continue working through this process up to the current month.
This write-up explains reconciliation in greater detail: https://quickbooks.intuit.com/community/Getting-started-with-QuickBooks/How-to-Reconcile-an-Account-....
You've got this. I'm here to help if you have questions about this info or anything else in QuickBooks. Enjoy your day.