How do I play halo 3 with people who aren't on my friends list?

[Some guy.]

I have xbl gold but in matchmaking or co op or etc it only let's me select open party. Meaning they have to be friends or have played with me before. How do I play with strangers?
Guys matchmaking doesn't let me search only make games for open party can some one make it detailed like - matchmaking then press this this and this

 

[vailance]

yea matchmaking, pick a game, and then wait up for everyone to gear up

 

[ninpo16]

that's fine just go to start matchmaking