Medial Exam include Physical Examination like Weight, check you heart and vision, blood pressure ..etc , X-ray and laboratory Test
IRCC will send you a letter via email to do the exam you should print it and take with you also they will give some instructions on the letter and what to bring with you.
Depending on your country you can check and find your Panel Physician
Here is the like to find where to go when IRCC request your medical exam :
https://secure.cic.gc.ca/pp-md/pp-list.aspx