Most medical schools require the following for admission:
1. Undergraduate degree including a year of biology, general chemistry, organic chemistry, and physics. Some also require English, calculus, or biochemistry. A high GPA is expected.
2. MCAT exam. (Medical College Admission Test)
3. Applications often include a review of extracurricular activities and an essay.
4. An in person interview.
Medical School itself is a 4 year program - traditionally 2 years of basic sciences and 2 years of clinical rotations (though some schools vary the mix)
Obtaining a license to practice from a state requires passing the USMLE (United States Medical License Exam) and completing at least one year of postgraduate training.
Post Graduate training - After medical school, the minimum training is one year of internship. However the vast majority of physicians do a full residency specialty training which lasts from 3 years (eg internal medicine) to 7 years (eg neurosurgery). After successfully completing residency training, passing an exam is necessary for Board Certification.
Many physicians go on to do sub-specialty training (eg cardiology after internal medicine, cardio-thoracic surgery after general surgery) which adds several more years and is followed by a sub-specialty exam for Board Certification.
At this point a physician has finished preparation to enter practice.