KA hasnt had any official events yet though one did start up by accident last night for about thirty minutes.
It was a PvP event. Straight up attacking rivals and the top 500 win a prize. You check the CC and MW forums for an idea they both had their PvP event this weekend.
The other type of event is more a chance/gambling style event and gold/gems being used does NOT gaurentee that you'll win the main prize. Here's a link from CC's first event, the items change but the format is the same.
http://www.funzio.com/forum/showthre...ht=Event+guide