What is a gacha event?

It's basically a blind bag style adopt event! You purchase a "spin" (ticket) for a chance at one of the ones you're interested in, and when it's over there are numbers generated for all participants and prizes are handed out. You're allowed to trade or resell yours (for the same price of the ticket) once it's over if you're not satisfied, and I believe there will even be a trading hub/journal set up for people interested in swapping once it's over. Also, there are only enough tickets handed out so that everyone is guaranteed a prize - there aren't any excess tickets, so everybody who plays gets something!

There's a really nice further explanation (plus the rules) of how it works in last year's event:
https://www.furaffinity.net/view/18097847/

Ohh I'm also very exited for this one