No problem!
Basically, the Retail method is an easier way of payment during trading, and it prevents scamming a bit better.
In our scenario, you would go to your town Retail and buy out/remove all of the furniture up for sale (if there is any). Then, you would fill up your whole Retail with something small (like a town fruit). You would put each item up for the max, 999,999 bells. Then I would come in and buy the fruit. You would occasionally have to put up more fruit for sale, and I would have to keep going back and forth from the post office to get bells, but you would basically get a million bells per piece of fruit, making the process a bit faster.
When I buy the items, the money will go straight into your bank account once you talk to Reese. The money will then appear in your bank account the next day.
I hope I made that clear xD