To a certain extent skills in eve branch out from core skills in each skill group. There is a whole group dedicated to trading. Some skills improve at a greater rate than the starter skills before it. For example, Trading lets you have 4 more sell orders at a time per level, Retail allows 8 more per level, wholesale allows 16 more per level, and tycoon allows 32 more per level. Skills modify other aspects of it too.

Broker relations reduces the fees you pay when putting an item on the market.

Accounting reduces the tax on all deals

Remote trading lets you trade further and further away from where you actually are.

The list goes on you can read what all the skills do at the Eve-Wiki http://eve-wiki.net/index.php?title=Trade_skills_overview

or at the item database on the eve website or at battleclinic.com

I hope you'll find the economy in EVE much more complex, diverse, and largely player driven to be more satisfying then the one you interact with in WOW and come join us.