At one point music thought it should tell stories; at another, it thought it represented pure emotion. These days, each composer embraces his or her own unique mix of beliefs regarding music's expressive and communicative potential.
Steve Reich is a minimalist composer who uses repetitive patterns that evolve slowly in time. In some it produces an altered state of reality, in others, anxious boredom. It depends on your drug personality: are you into transcendental experiences, or are you a speed freak?
This piece, "Music for 18 Musicians", has a generic, abstract title that doesn't give you a preconceptions. Like calling a piece "Sonata" or "Symphony" it refers to concrete facts about the piece more so than what it is "about". This allows you to follow your ear: do you find yourself listening to the shifting and overlapping patters, or does the music paint a picture? If the latter, what picture?
Here's the first part. It's up to you to find the subsequent parts.