First go to Jinx View on map - you have to go there with a party of 4 people.
You will have to choose between three stages: easy, medium and hard. In this tutorial we used a easy stage as an example.
You with your all party members will be teleported to an Dungeons island on which you'll have to kill group of monsters. If all monsters are killed then a boss will spawn on position of last monster has been killed. After you kill a boss you'll be teleported out to get a reward for participating.