There are three different game modes you can play in.
Practice: You can practice here to improve your game without losing any EPs. Before you start, choose your opponent’s difficulty. Keep in mind there isn't a crate reward in practice mode.
Team Fight: In this mode you will be playing with one of your friends or a random ally against two opponents.
Solo Fight: In this mode you will play solo against your opponent.
You need a team in order to play any of these modes. To build up a team you can choose up to 4 warriors.
Don’t forget that you need to finish the tutorial to unlock all game modes.