EVERYTHING YOU EVER NEEDED TO KNOW ABOUT: CLANSAt it's most basic, a clan is simply a group of people that regularly play with each other.
Most successful clans, though, are organizations that have loose sets of rules governing the actions of it's members,
and at least a few people that lead the group and determine the overall direction of it.
Being a member of a clan is being a member of a team. Your clan mates are people you can
look to for advice, training, and competition, among other things.
The entry requirements for a clan are determined by the leaders of the clan.
Most clans I know of, simply agree not to ditch the group after half a week and you're in.
Some may have more entry requirements though, such as having to beat the clan leader in a duel,
agreeing to follow a code of conduct, or making your personal armor color screaming neon pink.
If you are a member of a clan you should have a clan tag. Clan tags are important for this reason:
Having a clan tag allows other members of your clan, and the general public, to identify you as a member of a clan.
Some games have clan organization built in. Others, like Red Eclipse, don't, so, to have a clan tag you must add it to your username.
Generally, you shouldn't add a clan tag to your name without being a member of the clan in question.
Red Eclipse has a small playerbase, therefore, it has only a few clans.
Clans I know of: Wazu, and Evolution. I tend to see a few Wazu members whenever I'm online.
Large clans can have several sub-groups, like having a clan within a clan.
As far as I know no clan in Red Eclipse has grown that large yet.
As TristamK has said, there are occasionally clan wars on the password-locked servers.
Most clan wars involve the most experienced members of two clans duking
(google chrome suggests I cange
duking to
nuking. 
) it out to determine who is superior.
Nothing, it seems, is better than a little bit of friendly competition to get the adrenalin pumping.
I lost the game.