Who is Anonymous?
In the beginning Anonymous hacked as pranks, more to say they could than to actually stand against something. Since then they have transformed the leadership of Anonymous which has lead a much more activist role. They have taken part in many international hackings, and speak out against different political issues.
Anonymous is everyone and no one. Anonymous is you. You will not be denied your right to free speech, free press, free association and your universal right to freely access information both in real life and on the internet.
As for the literal operation of Anonymous, becoming part of it is as simple as going onto its Internet Relay Chat forums and typing away. There are numerous Twitter accounts which claim to be affiliated with Anonymous, and more websites that post and repost (known as mirroring) Anonymous content than there is room to mention here. The real-life people involved in Anonymous could be behind their laptops anywhere, from an Internet café in Malaysia to a Michigan suburb. Anonymous appears to have no spokesperson or leader. One could participate for a minute or a day in a chat room, and then never go back again.
(Information sources from CNN articles.)