In this scene, the prosecution suggests (based on the avaliable evidence) that Andy shot his wife and her lover without expressly accusing him of doing so.
In this scene, Andy takes a drink before confronting his cheating wife. The scene cuts to the courtroom, where he is explaining to the prosecution what happened that night. Then, the scene cuts back to Andy's confrontation.
After the principal caught Sams fooling around instead of being in class, he walked into the bathroom and saw that all his other friends were there. As a punishment, he wanted them to sing the school anthem as it shows that they have been learning something but they sung it with easy and with a different rhythm which surprised the principal. He learned to accept the song and approved the changes with it.