Mandatory is a synonym of required. That is, their meanings are nearly identical. An example, "The professor made the final exam mandatory for all students." Enforceable is for a rule, law, or regulation that is able to be enforced by a person or entity with power to do so. You could have a law or a rule that is mandatory but not enforceable. For example, a country could have a mandatory rule that at 1pm everyone think of a big yellow bird. Even though mandatory, it would not be enforceable because it would be impossible to know if someone thought of a small, blue fish instead. I hope that makes sense, :-)

No, they do not. Mandatory means you have to do something (in order to comply with the rules). It's mandatory for nurses to wash their hands before treating a patient. Enforceable, like many "-able" suffix words, means "able to be enforced". In other words, while we can make a rule, it might not be something we can actually enforce. In a dictatorship, they might ban speaking badly about the dictator. Is this enforceable? Not really. We can't listen to every single conversation everywhere in a country! However, that dictator could ban negative press (that is, ban bad opinions about himself from being published). That is enforceable, since the dictator can easily have all the newspapers read and punish the people who speak poorly of him.