Clans:
ThunderClan
ShadowClan
WindClan
RiverClan
SkyClan
BloodClan
The Tribe Of Rushing Water

You can also choose to be these ranks:

Deputy
Warrior
Apprentice
Elder
Queen
Kit
Loner
Rogue
Kittypet
Prey-hunter
Cave-guard
To-be

And, the first 7 people to comment the clan/tribe name they want to lead (if it is not taken) get to be the leader of that Clan/tribe. Unless you're in StarClan, or the Dark Forest. Nobody really leads those. And, this takes place at the Lake. During leaf-bare.