Currency is an item specifically used to trade for other items or benefits. Different forms of currency allow for purchase of different types of items. The two types of currency are gems and coins
Gems are the main form of currency Mineplex uses, mini-games or otherwise. Gems are basically the coins of some other video game you might play, whereas Treasure Shards are gems or diamonds. Gems looks like gems, and you can earn them by playing games. You always get 10 gems for participation, and 10 for the winning team. Other things, like kills or flag captured or first blood, vary from game to game. You can also get it by voting, parkour or registration. Gems can be used to buy in-game items, like kits. Kits usually cost 2000 gems for the first kit 4000 for the second, and on some games, more if there are more kits.
Treasure Shards used to be called "coins." Treasure shards are much, much rarer than gems, and can only be earned by chests and options in Carl the Creeper. Treasure shards can purchase some items in the menu, such as Morphs, and can also buy Chests that can give you even more effects.