Self Harm

I never understood self harm. I don't know why people do it, to get off on something, or they think they can't take the pressure anymore. Please someone explain why people do self harm. I can't compute why people would and most of the time I don't know why people do what they do. I don't know why people feel the way they do. So why self harm, what will it do to help the situation. I did self harm, I chocked myself, to see why people do it. I still don't understand.