The bill detail section displays the entire bills to be paid to the entity you have selected while creating.
After creating a bill, you have to click on "Allocate" to add a specific account to the bill which comes under the entity you have selected and you can also "Refresh" the bill if you made any changes in expense accounts after creating the bill.
Once payment is done through Receipts and Payments, it will automatically update the "Payments Made" tab with Transaction details.
You can also add files related to the payments in the "Files" tab.
Once the Grand Total matches with Bill amount you can click on the action "Validate" to complete the transaction. And once the bill is Finalised , it cannot be reverted back to another state and is locked permanently. Syncing with Finance systems will happen only after the is finalised.