There are a large number of instruments in the West Side Story orchestra with particularly large woodwind, brass and percussion sections.
As is common in theatre pit orchestras (or bands), the players in these sections often play more than one instrument. This is known as doubling.
'Something’s Coming' is taken from Act I and is Tony’s first solo. At this point he has not met Maria. He has become disillusioned with gang warfare and looks forward to a better future. He wants to leave the Jets but agrees to join them to go to a dance later that evening.
The song opens and closes in D major (a key signature of two sharps). It modulates (changes key) to C major for two contrasting sections of the song.
The interval of a tritone is central to the West Side Story score - it helps to hold the work together, linking various musical themes and acting as a symbol of tragedy.