Understanding CIO

I am a FTM and I have never heard of the cry-it-out method and I am just so confused, maybe I’ve got the wrong idea. My LO only wakes up at night because he is hungry, no other reason. So for those who do the CIO method, are you making your hungry baby cry themselves to sleep because you don’t feel like feeding them when they are hungry? Or do you just have babies who cry for no reason at all? I’m genuinely confused about the concept.