Murden

hi i have recently bought arma 2 operation arrowhead and i have been on the missions to know the controlls a little better and now im looking to play on multiplayer. although if i try to join a current game it always says i cannot connect. i think i need the latest patch if someone could provide one and where to put the patch that would be great! also if anyone can give me general tips and point me in the right direction that would be great. :)