To promulgate is to officially put a law into effect. Your state may announce a plan to promulgate a new traffic law on January 1st.
Laws aren't the only things you can promulgate. The word promulgate comes from the Latin word promulgatus, meaning "make publicly known." Someone can promulgate values, belief systems, and philosophies — it just means they're promoted or made public. For example, you might write an article to promulgate the benefits of eating only organic foods.