What do I need to do to become a doctor?

I am in high school and am looking at colleges and I would like to be either a doctor or an agricultural manager. I will ask a separate question about agriculture, but for being a doctor, can someone give me detailed information as to what I need to take in college to get into medical school, how long I need to be a resident or intern, and how long it takes before I can start my own practice. I would like to be either an oncologist or a general surgeon. I love science and love to do service and help people. So basically, tell me what I need to do (or what most doctors do) until I can start my own practice. Thanks.