There is a new defense in FIFA 12 known as 'contain'. What does it mean and how do you use it? I played the interactive tutorial, but I don't get the idea.
I don't have a copy of FIFA 12, but here's the meaning of "contain" in real-world soccer:
The idea is that a defender should "manage" an attacker and wait for the attacker to make the first move instead of rushing forward to tackle the ball.
A defender trying to contain an attacker will typically hang back a bit, move to one side or the other to try to force the attacker to go in a particular direction, etc. The theory is that once the attacker makes their move, the defender can react appropriately.
You would typically apply it when play is relatively slow around your net. If there is a lot of fast-paced passing going on, you're likely better off moving around quickly to keep up with it.
Far as FIFA 12 goes, it appears that you'd basically use it in similar situations. You shouldn't overdo it:
In addition to Anna Lears great answer an answer more based on personal experience:
I found containing most useful in situations where you are following a winger towards the corner flag. Normally he will be sprinting, so you have to sprint as well to keep up. The winger usually has 3 options:
It's very hard to anticipate which option he will choose, pressing contain helps you to cover all of them, because your defender reacts automatically to the movement of the attacker.
It's also a very good way to stop opponents focused on dribbling rather than passing. Without containing, you will have a hard time stopping someone who is using precision dribbling with Özil, because the manual reaction time normally isn't enough to counter the quick hooks an attacker can perform.