How do i get 4 players on halo 3 campaign?

[kane f]

I have xbox live but i don't know how to get 4 players on campaign mode.Do i have to have a party with players over xbox live?I don't know what to do.The same goes for forge and custom games.

 

[Loki]

Invite friends or have an open party. With campaign and forge, invite your friends. With the others, you can have the match open and anyone can join. I learned this the hard way when I was rocking in a match when some random guy came and blew me away. was kinda funny...