How might I go about writing a Book?

I've recently started to tap into my poetic side but its strange its seem to have develop into a philosophical side and I've been pondering writing a book. I don't care about being publish or anything like that but to just say that I done it. I want to write a semi-autobiography about my abstract and/or reflective views written through the eyes of a teens daily events I'm still brainstorming for a good title but I just wanna know some ideas of how I could or should write this book..... Oh and btw I'm a 17 year old highschool student inspiring to become a doctor... Just to give some insight on me