Hi kenney, this is my very first game jam, it was fun and exciting, but i don't know if there are a reward for the winners, or how do we know who are the winners

Congratulations on finishing your first game jam! :)

Right now the jam is in the voting period, after which the results should be available afterwards. I don’t remember right off, but I think there is a results tab that will appear on the jam header next to submissions once the voting period ends. After the voting period you should also be able to see your entires results on its submission page as well.

As for prizes, there are no additional prizes for winners beyond the creation of the game itself (source).