There are two ways to submit medicals.
1) Upfront Medicals: you can google for physicians for Canada Immigration in your area and book an Appointment. You should pay the prescribed fee and get your medicals done. In the end they will provide you a document with UMI Number. When you apply for Canada visa attach this document along with all your other documents.
2) Medicals after application of Visa: You can Apply visa without medicals. IRCC will later send you an email to submit your medicals. You should go to Canada Immigration Authorised Physician in your locality and pay the fee, get the document and upload in IRCC website(GC key - your account).
You can do any of the two. Go for medicals before visa application or after visa application when IRCC requests you to do.
One suggestion from my side, when posting question in this forum. Please provide few more details like which country, city you are from which intake etc... so that others can help you better with more info.
