What is a Raffle Ticket? I've found one recently, but I don't remember how I can use it...

You can either sell it to another user, or redeem it for either a small amount of CSC or a random (cheap) Cash Shop Item.

ok, thanks, now I remembered that thing... and what amount of CSC I can get?

any, not much though,... recently received around the 15 CSC, .... xD

Yeah, I think it might be under 25 CSC? There might be some cheap Cash Shop Items that make it worth the risk, if you're lucky though. There's also an achievement for using one.