The primary rules are that you can only possess marijuana purchased from licensed dispensaries in approved forms. Also, you can only consume medical marijuana in your home or another private place. Finally, employers can permit cardholders to use medical marijuana on-site but are not required to.
Cardholders are bound by the state's other marijuana laws, including intoxicated driving, public consumption, and possession of marijuana obtained outside the limits of their cardholder rights.
Patient status does not exempt you from federal cannabis laws either. It remains illegal to transport cannabis across state lines.