MD is the Post Graduate degree(3 years course) for medical Graduates(MBBS) that deal with the branches which do not require Surgical skills. MD is awarded in Non-clinical as well as Clinical branches.

Non-Clinical Branches for MD are- Physiology, Biochemistry, Pharmacology, Forensic Medicine, Community Medicine, Microbiology, Pathology (the last two are usually considered para-clinical)

Clinical Branches for MD are- General Medicine, Paediatrics, Anaestheiology, Radiology, Dermatology, Pulmonology(TB and Chest), Psychiatry.

MS is the Post graduate degree(3 years course) which requires surgical skills mendatorily. 

The only Non-Clinical Branch which gets a MS degree awarded is Anatomy.

Clinical Branches for MS are- General Surgery, ENT, Ophthalmology, Orthopaedics, Obstetrics and gynecology.

DM is a Super specialty Degree which is awarded even after doing MD. For this you even have to choose a particular system from the branch in which you did MD. I”ll give you example: if you are MD General Medicine you can do DM in Nephrology, Cardiology, Endocrinology etc. There are many branches.

MCh is equivalent in terms of Super Specialty degree which is done after MS only and has similar criterias as DM.