Depends on what you want to do.
Snapshots don't need registration.
Friday Squad Ops has a forum dedicated to that event, and instructions on participation.
Scenarios run generally each quarter, and have instructions on registration as well.
Events information is at
www.ahevents.org this is where the rules write ups are kept, and registration for the various events.
Spend some time browsing the various event forums, and jump on in. You'll have a great time.
Also, the tools to form squads in the SEA are exactly like in the Main Arena. They are an independent squad though, dedicated only to the special events arena.
