Onetime fee

[poidoggy]

I'm a part time seller without a store. It's difficult for me to keep up with all the changes and when I see new things appear on my account, it doesn't tell me why they are there. For example, I looked at my Seller Hub and saw there was a "Pay your pending balance" under a sale I made. I looked at it and it shows that I owe a few dollars and some change. What is this? Why is this? I'm sorry if this is a repeat question, or I should look in the fees FAQ. The selling fees FAQ is very confusing and lots of density and can't find exact answers there. Thanks for any help.