The 8K is the value of goods sold on amazon in that month from my referral link - I think I got about $350 in commission.
These are not advertising fees but direct commission for products sold. When someone comes to one of my hubs, clicks on one of my amazon links and then buys something I get a % of that sale.
The % ranges from 4 - 10%. Some items such as electronics have a fixed percentage (4%), mp3 downloads (10%) - but the rest of the items have a variable % based on the number of items sold. The more you sell the better commission % you receive.
I've been focusing a lot of writing product hubs because they just seem to earn so well - give it a try!