Paty, you pay $.20 cents per listing. This is charged when you list the item, billed per month (normally due the following month). So if you list something in December, the bill for that $.20 cents is due January. You have two pages of listings. The $6 is from your listings.
You need to pay this bill. It is for listing your items. If you don't, you might have a disruption in your shop.
I hope that clears it up. Good luck with your new shop!