What to do to get a PR card if yiu are a us citizen marring a perminant resident?

You need the documents that are required by the state in which the marriage is going to take place. Usually it is a legal form of identification and age (birth certificate, passport, etc.) SS card or letter from SSA in some states, "green card" or fiance visa, and such as that. Contact the local office where marriage licenses are issued to find out the specifics for the state where you want to get married.