Any of these texts would be a good introduction to the ideas and terminology of post-tonal theory.
Straus, Joseph N. Introduction to Post-Tonal Theory 3rd ed. (Englewood Cliffs, NJ: Prentice-Hall, 2005).
Rahn, John. Basic Atonal Theory (New York: Shirmer Books, 1980).
Forte, Allen. The Structure of Atonal Music (New Haven: Yale University Press, 1973).