Is this to use while you're actually playing, or to analyze previous hands, or just to mess around with to get a better idea of the different EVs?
No, don't use it while you're actually playing as many in game ICM programs violate the terms of service agreements of the sites you play at.
However, it is legal to use these programs to analyze your play after the game. Use ICM calculators to give you an idea of how good your play was, and what good plays would be.
The idea behind using ICM is that your tournament chips have diminishing marginal utility. So you can't just use simple pot
odds to analyze your play. ICM is a model that essentially assigns a value to your (and everyone else's) stack of chips.
SnG wizard automates the various calculations used to assign value to tournament chips, and can run various other calculations at the same time.
So, for example, if you had AK on the button. If you input the stack sizes, the players remaining, the prize structure, and the calling ranges of the SB & BB, it will tell you if your shove was +EV or not.
ICM doesn't take into account the skill of various opponents, and it mostly works in scenarios that are close to the button, or in the final few places that pay out. However, its a hell of a lot better way to analyze your play than using
pot odds.
