I saw it in more than one forums, people just gather up, having ranks.
what they do? why should i join one?
and befor invitation start swarming here, ill get my first 'rivate' rank two mounth from now, in a very big clan. it called IDF. so for now i prefer to stay a regular citizen.
Clans in MMOs will wage wars with other clans. Or they'll explore games, compare ranks, discuss different subjects, or just hang out in general. If you like hanging around with other people or want help with defeating enemies in games, they're good.
You could say we're part of the AG clan and the Kong clan is our enemy.
I recently joined a clan in Battlefield 3 so I have more people to play with. Playing alone is extremely boring and you'll usually end up on the losing team. It's more fun when you have competent teammates.
I can't really explain what I clan is because I hardly know myself, but there are groups of people that share a interest in a subject the clan is advertising (music, AG3, etc). You can join by looking at clan widgets and seeing the leader of the clan (usually the clan will say who is the leader if the clan is well established). The leader will determine if you can join or not and what you do inside the clan. As simple as that.