Vídeo com explicação: https://www.youtube.com/watch?v=QTu03baHmWw
Link 1: http://baladre.info/english/sedaviwebfront/mustshould.htm
Link 2: http://www.englishexercises.org/makeagame/viewgame.asp?id=6270
Link4:
http://www.englishforeveryone.org/PDFs/Modal%20Auxiliary%20verbs%20-%20Must%20and%20Have%20to.pdf