It´s a beginning to start playing poker, in 0.25c you can learn the basic , about poker, and the general idea of ICM. But, your question sounded ambiguous for me, do you want to learn how ICM works, or the definition/ application of ICM? I would recommend you to read this thread: https://www.cardschat.com/forum/tournament-poker-59/anyone-simplify-icm-245516/