How does the 48 hour halo 3 xbox 48 hour trial work?

[Cristion]

I got the game and it says 48 trial, so does it activate when i play the game or does it activate when i got to matchmaking?

 

[sexbox live]

there is a card in the box that has a code on the back
and basically you say join xbox live and out that code in, yadda yadda yadda
and then youll be on xbox live
(not for very long)
but yeah, there you go