1st step: Complete high school with good grades
2nd step: Complete a 4 year undergraduate university/college degree with good grades
3rd step: Complete a doctorate program in the field of choice (examples below)
Doctorate in Medicine (MD) or Doctorate in Osteopathic Medicine (DO) - use medications and surgery to treat almost anything-basically, become a medical physician
Doctorate in Dentistry (DDS) - treat problems involving teeth and gums
Doctorate in Veterinary Medicine (DVM) - treat animals using medicine or surgery
Doctorate in Optometry (OD) - deal with issues involving the eyes
Doctorate in Podiatry (DPM) - deal with issues involving the feet
Doctorate in Chiropractic (DC) - deal with issues involving the spine and neuromusculoskeletal system
4th step: pass national and regional board exams governed by whichever field you have chosen
To become a doctor, get high grades in high school if you can, especially in your science and math classes, and do service hours, which are hours you spend outside of school, usually during the summer, dedicated to community service. These help you get accepted to a good college. Ask your guidance counselor about it. Do well on your SAT and ACT, do great on your OGT, and take interest in science, math, health, body, and academics in general. Make sure you take more science and math-based classes in high school.
For those very dedicated to becoming a doctor, reaching out to a doctor to get the low-down would be smart. There's a site called Wisewords(.co) has lots of doctors 'standing by' to share their insights on how they got to where they are. Highly recommended you check them out.