I hope I got this all right.
ICM helps you make bubble decisions based on your prize pool equity.
Here is an example:
$10 10 player SNG, 4 left, pays out 50%, 30%, 20%
Stack sizes are all the same, so we have 25% equity.
All in in front of us and we figure to be 60-40 fav.
Our equity if we double up will be 38%. (This is where you do a bunch of math or use an ICM calcuater, of course I used the calculater.)
So... 60% we win 60 x 38 = 2280 /100 = 22.8
40% we get bubbled = 0
ZOMG! our equity dropped from 25 to 22.8 so making this call costs you $2.20 vs folding.
There are several good articles on this of which I won't post a link since some are at other forums, google it.