Hey I got this ga,e yesterday I don't even know how to play it online :S, If u know how to play the multiplayer mode just tell me plz

The online multiplayer mode is no longer available. Same goes for most Ubisoft titles of that era.
However, there is a way to get around this, set up a VPN with your buddies, log in and choose "LAN" under multiplayer.. You can also use LogMeIn Hamachi: https://secure.logmein.com/products/hamachi/

I wish STEAM informed buyers of this game better that the online Ubisoft servers are gone, especially since they advertise this game as a multiplayer experience.

I'd advice to look into VPN/Hamachi, since there are more games that can benefit from this "workaround", to be exact any game that you can play over LAN.