What is a personal statement?

I am struggling to understand or like DON't know what i am suppose to write. AM i suppose to write about why i want to go into this field or write about WHO I AM, and even if it was to write about WHO I am .. then atleast what part of myself am I suppose to write, like does it have to be related to the major I am pursuing or not? PLEASE ANYONE, HELP ME OUT HERE, I AM SO CONFUSED.