Step one: Breathe in
Step two: See a man get a cigarette in the eye before you can move
Step three: Get banzai charged and die
Step four: Get banzai charged and die
Step five: Get banzai charged and die
Step six: Get banzai charged and die
Step seven: Breathe out
Step eight: quit the campaign

Step one: Breathe in
Step two: I haven't played the multiplayer and don't know how to help
Step three: Sorry :(
Step four: Breathe out

Step one: Breathe in
Step two: Kill zombies
Step three: Run out of "♥♥♥♥ to kill with"
Step four: Get Ray Gun from the box
Step five: Get downed in front of your Ray Gun
Step six: Breathe out
Step seven: quit the game

Congrats, you now know how to breathe while playing Call of Duty: World at War.

Have a fun time raging your ass off :D