So I have two accounts, then?
Absolutely correct. You have your BartAccount, where you pay for work, or for goods, and where other members pay you for your work, or for your goods. And you have your Europot, where your commission is collected from.
Your Europot can't go into the red. If you run it down, you won't be able to pay anyone, and you will need to top up, via PayPal, with a minimum of 5 Euros.
Your BartAccount is the really useful one. You have to remember, Barts cannot be changed into, or from, any other currency. You have to use them to Barter with other members.