Can someone explain what Comic Con is to me?

I know its about comic books, Im Irish so Comics and this kinda stuff isn't really big in Ireland. Anyway a while ago I went to Australia and one of the boys I was living with wanted to go to something called SuperNova, so I went along for the bant, it was pretty cool I seen people walkin around in Predator suites and stuff, im not to into comics and stuff but I bought an Iron Man one. I was just wondering is Comic Con anything like supernova? Where is it on, how do I get tickets, is it expensive and what kinda stuff can you do there? I'm fairly open to anything to be honest. il do whatever if its fun.