Missions are tasks you can do that appears often to you realize. You can do /dismiss if you are busy,or if you don't want to do them.
Types
Kill: You need to kill a specific number of random mobs. For example: Kill 3 Zombies in 48 Seconds.
Loot Chest: You need to find a specific number of loot chests. For example: Find 6 Loot Chests in 457 Seconds.
Duel: You need to duel a specific number of players. For Example: Duel 2 Players in 125 Seconds.
Reward
The reward can depends on the time,or in the amount. And it have 2 Types of Reward: Emeralds or xp. If it is very easy,it can be a low reward. If it is hard,it can be a high reward. For example: Duel 1 Player in 543 Seconds. Reward is 27 xp Kill 1 Undead in 150 Seconds. Reward is 543 Emeralds