You cannot trade here in any traditional sense of the word.  It runs more on a consignment program.  You need to use the market to buy or sell goods, and a few select things can be found for purchase at various general and weapon stores.  

Here are some links I strongly suggest you check out.

http://larkinorguide.com/help

 

Market transfer Guide 

http://forum.flyordie.com/thread.jsp?forum=13&thread=26950

http://dictionary.com

Good luck, happy clicking :)
TeT