So i hear you want to make some cash. Well, there are several ways to do it!
Selling items is probably the easiest, just use /sell and right click a store that sells the item you want to sell. Easy!
Trading. Since this is an economy you're free to sell your items to other players or trade for other items, this way you can get great deals!
Killing monsters. In this server, monsters drop money when killed, the harder the monster the more money! Finally, creepers give you more than just gun powder!
Player vs Monster Tournaments, i host these often at the Colosseum, it's a great way to earn some easy cash, with cool bonuses
Player vs Player Tournaments, if you want to have one of these, round up some friends and ask me to host at the Colloseum, you need 3 or more people, and last standing gets big cash reward
Duels, offical duels are held at the Colosseum whenever you and a friend/enemy want. Just ask me and i'll sponsor it, winner gets 50 coins
Spleef Tournaments! These are also hosted at the Colloseum, spleef is a fun game where you try to dig the ground from under your opponent to make them fall into the pit under the colloseum
Winner gets 200 coins, requires 3+ people
Those are some of the major ways to get money, I'm sure you can think of a few more ways if you put your head to it