IVE been playing halo 3 in matchmaking but now i need to figure out how to join a game as a private or whateve

i just need to fugure out how to join a game. it should be easy i kno but i cant figure it out......just want slayer

IVE been playing halo 3 in matchmaking but now i need to figure out how to join a game as a private or whateve
not sure what you're asking, do you have your xbox live gold membership active?. if yes just go to matchmaking and just wait for a game