If you are selling a resource or service then post it in the appropriate category. When you are posting remember to post your game name and a location so that buyers can contact you along with your rates. Say you are selling Hydrogen, you would post " I am selling X amount of hydrogen for X amount of Credits at these ranks. My game name is X and I can be reached at [x:x:x]".
If you are selling a service i.e you are willing to join their alliance to help with a way you would post (in the Freelancer category) something like " I will join your alliance and help you fight the war for X amount of credits or other" . If you had any conditions i.e. will not attack any members of MY alliance, make sure to post that too.
A freelancer is someone who is willing to do a service for a payment. A freelancer can be hired to help fight a war or help train an upcoming alliance, or how about a hired gun, a hit man if you will. If you can come up with a service that you can sell you can be a freelancer.
A Ship Pack is simple resources that you are willing to sell OCH that will build a predetermined number of ships. and example would be, if I wanted to sell a ship back of 100,000,000 Zeus' or 1,000,000,000 Hades'
then you would sell the Ore and Crystal and Hydrogen required to build that many of those ships to the buyer.
How to trade,
When you find a package you would like to buy whether it resources or a service you would contact the the player in game (game name and location should be provided by seller in post) and make sure that the deal can happen in the time you agree to. After you both agree on the deal you (seller) will send a message to BFG support (in game bottom of page) and ask them to transfer x amount of credits to (game name of seller).