This article is too damned short, Marine! You will help Gruntipedia by so it will fit the screen, fool!
Theater is where you can watch all the video's of you that hidden Jackal recorded behind your TV screen, that means it masturbated to the times you t-bagged other players.
Well sonny, the first thing you'll need to learn about theater mode is the screenshots. If you time it just right and all that, you could get a really dope ass screenshot that looks like this, or you could be a noob and take a screenshot that looks terrible and think its great by putting it on your file share and going into matchmaking yelling through your mic, "ZOMG EVERE1 L00K AT MAH D0P3 SCR33NSH0T!!! IT R RLY D0P3!!". Then have everyone laugh at you. You don't want that do you? No, so don't do that. But now with the release of Halo: Reach Around, nerds, geeks, no lives, and your dad have been wasting their lives in Forge making "Anime Girls" out of weapons and other forgeable shit then taking screenshots of it. Sometimes it may be stimulating (very rarely), but you shouldn't do that because nobody gives a fuck about your imaginary girlfriend. Also, you'll like hot girls in real life a LOT better, trust me.
The next thing you'll need to learn about theater mode is the film clips, you can film anything from a perfect snipe to when you t-bag a marine and he/she says something funny. But, just like Screenshots, noobs abuse this power and annoy people with "Z0MG A P3RF3CT SNIEP!!", even though it sucked dick. Do not make a film clip unless your absolutely sure it's perfect, even if it means wasting your social life to do it, it is your destiny. If you don't do it, I'll find where you live and beat the motherfucking fuck out of you. So do it, bitch.
Here is a gallery of some of the dopest, funniest, and awesomest screenshots ever. You may add to it.