Sooo... basicly... this plugin adds money to your Minecraft server.
Money that can measure items in game.
For example if a diamond is the hardest item to find in the game then it's price would be 10$
If the dirt is the easiest it's price would be like 0.01$
And this prices will not be set by the administration of the minecraft server, but from the comunity itself!
If someone things that 10$ for a diamond is too much he wont buy any diamonds until someone lower the price to 9$ or something.
The iConomy plugin itself is only the core, but there are plenty of other plugins that connect to the iconomy and use its curency to buy/sell stuff and even earn money - like the Heaven Activity plugin we talked about early on.
Link to the iConomy: http://forums.bukkit.org/threads/econ-iconomy-5-0-1-eruanna-953.40/