You can list up to 15 items for sale, but if you list more than 10 the fee goes up.
When something you have listed is purchased you will see a message that says that such-and-such has been sold. An icon appears on the top-right of your minimap that tells you that you have money waiting to be collected. Mousing over this icon will tell you how much Kinah is waiting for you. To collect your money, return to any Broker, go to the Sold Items tab and click the Collect Money button. Any items that fail to sell within 8 days will be returned to you via the regular mail.
See also: Broker (for generic information about Brokers in MMOs)