ICM is not prone to being simplified. Many have tried, and all have bored the readers to death. You owe it to yourself to read through the whole treatise at least once, but only if you don't have high blood pressure, and are wearing a tin foil hat. That may help keep your head from assploding.
As to poker, ICM tells
you that stack sizes near the bubble are important, and that chips can be worth more or less than face value depending on those stack sizes. And it describes why.
I've never used this, but might soon;
It's an ICM based equity calculator.
Honestly, it's been over a year since I last delved into ICM much. There are several aspects of what I thought I understood, that have worked their ways into my game. But even then I knew that it was generally over my head. And I'm 6'3.5" tall!
Perhaps the simplest usage is in a sat where x players will qualify, and you are or are not one of them, and if you are you might find the best course of action is to sit out till the game ends.
Google Independant Chip Model Poker for a wealth of articles.