The story of Amadeus is about two characters, Salieri and Mozart. Both are composers that are alive at the same time, working in the same city. Salieri is the royal composer for the emperor. Mozart is a well-known composer from Germany who turns his back to his country and gives them the rear-end so to speak. Mozart comes to Italy to write an opera for the emperor and ends up staying longer. Salieri eventually goes mad from Mozart's childish ways and from his beautiful music!
Salieri is a well-respected composer for the emperor and is a hard worker for what he has. He prayed to god everyday that he would get better and write wonderful music. But as he got older he found that music was only a way for god to humiliate him and make him have a desire that he could never achieve. He wants to be everything that Mozart is but he will never become.
We see that he gives up on God in the scene when he takes down the cross and burns it, showing the camera angle from the cross's point of view in the fire looking at Salieri as "Mozart's view" looking as if in terror of Salieri.
Mozart is a miss-behaving young German composer whose works were already respected by Germany. As he leaves Germany he gets himself a wife that truly loves him and cares for him. When he gets to Italy he meets the emperor and all his men he gets asked to write an opera for them. He is very excited to write the opera and gets on it right away. Salieri checks up on him periodically to see the music and every time gets more and more jealous of Mozart's god given talent.