Step-by-step explanation:
Music is a very important aspect in the theatre. All the different musical elements can be used in many different ways, for example,
Lets say people are running from something in a play / theatre production, the music can be very important to emphasise whats going on at that precise time. For instance they could have the beat of the drum slowly getting faster to show that the bad guy is getting closer and closer, or they can have it do the opposite. There is many different ways they can "tweak" the music they are playing to fit whats happening on stage.
Musical compositions can evoke different emotions, once again by using many different musical elements and aspects. They can slow down the tempo, add in strings for emotion. They could speed up the tempo to build suspense and many other aspects and elements of music can be used to create more 'Feeling' and 'Emotion'.
Hope this answers your question. :)