When you use Credit Cards with QB things change a bit. First off each card needs it's own account in the chart of accounts. It has the option to choose "credit card" as the type. Then to enter (or download) transactions you would go to "banking" and choose "enter credit card charges". Be sure to select the correct credit card account if you have more than one! Then depending on how much detail you wish to enter fill out one for each individual charge. It's at this point that you assign the expense category in the "account" area.
Then when your statement arrives, you can "reconcile" the credit card with your entered charges. Quickbooks will automatically create a bill or a payment when you complete the reconciliation. Any questions?