When something comprises other things, it is made up of them or formed from them. The periodic table comprises 118 elements, because the whole comprises the parts.
In its traditional use, the word comprise is the opposite of compose: if A comprises X, Y, and Z, then X, Y, and Z compose A. But because compose and comprise sound so much alike, people have long confused the two. So now you often hear things like "The band is comprised of a guitarist, a bassist, and a hairy drummer," whereas sticklers would prefer "is composed of" in that sentence. The word is undergoing a usage shift, making it just as hairy as that drummer!