Whats wrong with my truck?!?

I just got my first car from my dad and it is in bad shape (1993 ford explorer sport). It drives fine, be when you are stopped are idling. BIG TROUBLE. When I am at a stop light I am constantly scared of it dieing on me like is normally does. When im stopped or idling the car is shaking back and forth and it constantly sounds like its going to die and i usually does. But when im actually driving its fine. I have no idea whats wrong with it and im very scared to drive it. Do i need a tune up? or an oil change. Please any help!