We passed a constitutional amendment to allow medical marijuana for certain specified conditions. You will need to read the amendment to determine whether or not your conditions are on the list. If you have a condition on the list, your doctor will need to sign a form verifying that you have said condition which you will then take to the department of public health to apply for a permit. You pay the fee and are issued the card. The health department is currently issuing cards.
Theoretically, you now have the right to possess marijuana. Unfortunately, we have no dispensaries, so there is no place to obtain said marijuana legally. Permits were issued for growing facilities last month, but those permits are on hold due to questions about the process used to select the companies given the permits. Until the growing facilities are up and running, dispensaries will have nothing to sell.
Hypothetically, marijuana can be legally obtained from another patient, as long as said patient does not sell it to you. Of course, the question will come up as to how that person obtained the weed.
Truthfully, law enforcement and the courts are dealing with a whole new world here. I predict it will be several years before all of the cases wend their way through the courts and we have a stable policy.