There's a decent summary on wikipedia in the curriculum section:

Once admitted to medical school, it takes four years to complete a Doctor of Medicine (M.D.), or Doctor of Osteopathic Medicine (D.O.) degree program. The course of study is divided into two roughly equal components: pre-clinical and clinical.

Preclinical study generally comprises the first two years and consists of classroom and laboratory instruction in core subjects such as anatomy, biochemistry, physiology, pharmacology, histology, embryology, microbiology, pathology, pathophysiology, and neurosciences. Once students successfully complete preclinical training, they generally take step one of the medical licensing boards, the USMLE, or the COMLEX.

The clinical component usually occupies the final two years of medical school and takes place almost exclusively on the wards of a teaching hospital or, occasionally, with community-based physicians. The students observe and take part in the care of patients under the supervision of resident and attending physicians. Rotations (also known as clerkships) are required in internal medicine, surgery, pediatrics, family medicine, obstetrics/gynecology, neurology, and psychiatry. Beyond these, a variable number of specialty electives are required. Additionally, students are generally required to take a sub-internship rotation where they will perform duties at the intern level. During the fourth year, most medical students take Step 2 of the medical licensing boards (USMLE Clinical Knowledge & Clinical Skills [for M.D.], or COMLEX Cognitive Evaluation & Performance Evaluation [for D.O.]).

Many medical schools also offer joint degree programs in which some medical students may simultaneously enroll in master's or doctoral-level programs in related fields such as a Masters in Business Administration, Masters in Healthcare Administration, Masters in Public Health, JD, Master of Arts in Law and Diplomacy, and Masters in Health Communication. Some schools such as the Wayne State University School of Medicine and the Medical College of South Carolina both offer an integrated radiology curriculum during their respective MD Programs led by investigators of the Advanced Diagnostic Ultrasound in Microgravity study.

Upon completion of medical school, the student gains the title of doctor and the degree of M.D. or D.O., but cannot practice independently until completing at least an internship and also Step 3 of the USMLE (for M.D.) or COMLEX (for D.O.). Doctors of medicine and doctors of osteopathic medicine have an equal scope of practice in the United States, with some osteopath doctors supplementing their practice with principles of osteopathic medicine.