The full title of the musical/play is Les Miserables, a musical adaptation of Victor Hugo's novel of the same title. The music was composed by Alain Boublil and Claude-Michel Schönberg, and the lyrics were written by Herbert Kretzmer. The music would be performed by an orchestra and would include all sorts of instruments, including violins, drums, flutes, clarinets, various horns, piano, and others. You can read about the creation of the music and songs at the official web site, linked in the sources section below.
The genre of the play is a relatively new one, called musical theater. Before the creation of such musicals, opera provided the only dramatic musical performances. In the late 19th and early 20th centuries, such composers as Victor Herbert and the team of Gilbert and Sullivan introduced an alternative musical form: the operetta, sung in English. Out of this grew what we know today as musical theater, or the Broadway musical.
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If you are asking because your teacher has given you the task of choosing songs you like as background music or as a soundtrack, you will need songs that express anger for the inequality of the poor citizens in Paris; anger, sadness, and joy at the revolution for all who rose to fight, who died, and for those who survived to see a better day; joy at Cosette and Marius finding one another and deciding to marry; justice and /or shame when Valjean confronts Jalvert once more and lets him go; sadness at Valjean's death in the end just when it seems that everything is getting better for everyone.
I would think most of this will have a melancholy tone to it--lots of instruments can give that effect. Violin, flute, harmonica, piano.
Some will have angry tones--horns, synthesizer, percussion.
If you are asking about the musical already in place, the majority of these songs are big band musicals. Full orchestra music to create each of the moods created by Victor Hugo in the book.
I have included a link to the musical's homepage. Good Luck!
There is actually a musical for Les Miserables and their are even some sites where you can listen to clips of the music used. It's also very possible that you can hear and see scenes of this musical on YouTube.