From Section 1, Part I (Yes, I did get further along than this, the second paragraph, but figured I’d better start posting on it):
Epic poetry and Tragedy, Comedy also and Dithyrambic poetry, and the music of the flute and of the lyre in most of their forms, are all in their general conception modes of imitation. They differ, however, from one another in three respects–the medium, the objects, the manner or mode of imitation, being in each case distinct. (p. 1)
Basically, art imitates life. The medium, I am assuming is the presentation, played or written or spoken. The objects, text or brass pipes and strings. These do use sound–if text is read aloud–to communicate. Communicate what? Emotion, decision, ideas.
Aristotle goes on to inform of the harmony and rhythm employed in the various forms of art, including the rhythm or movement of dance to show emotion, character, or action. This can be seen when watching dancers perform to a specific piece, as well as the goings-on at the local disco where the patrons use body language to not only express their feelings about themselves, but to "speak" to a dance partner in the hope perhaps of further engagement for the evening.
I do intend to reread this section and the next few sections before going much further in posting as it seems that once understood, it will make everything else that much clearer.