(adsbygoogle = window.adsbygoogle || []).push({}); 1st dont call me a noob or stupid please cause im new (st technically i am a noob)

so can someone shed some light on me about clans and clan tags...
1st what are clans/what do they do/what are the point of them?
2nd How do you start a clan
3rd if someone makes a clan, and you just put the same name as your clan tag, does that mean your in there clan?

4th please tell me anything else you know about them
thx =)