How do you go about obtaining medical marijuana?

This is a long process, I will give you a short answer here though.

First, you need to live in a state that allows the use of medicinal marijuana. You also need to be diagnosed by a doctor with a disease that would warrant the use of medical marijuana. After you have done this the doctor will decide if this treatment is best for you and finally prescribe it if they decide it is necessary. I believe that in most states where the use is allowed that there are certain places you need to go, and generally they will give you an id card saying you are allowed to posses the marijuana for medical reasons along with you marijuana.