Your clan defines you, who you choose to represent. Each clan has their individual unique outfit.
To join new clans you must earn them during events held in game.
These are the three clans that you may choose when you first start the game.
These are the clans you may discover during special events. Clans are in order of their original release date.
There are 4 kinds of titles you can achieve with each clan. You get the novice suit after you earn the clan. You reach the second title when you gain 20 points with that clan, which earns you the novice suit. You get the grandmaster title when you get 50 points, which earns you the grandmaster suit. The guru title is achieved when you reach 99 points with one clan (there is no special suit for this clan).
Note: There is a new system for gaining clan mastery. Check it out by going to Jutsu System.