and i definitely wouldnt start with polytonality until you understand the basics of tonality/harmony/counterpoint...
but ill try to explain a few things...
i recently learned and analyzed like polymodal bartok stuff, from the mikrokosmos. it isnt that complex to understand. it is to play and compose but theorywise its basically two voices playing in different modes so you have a diferent tonality in each voice.
but then again his larger works and stravinsky's are much more complex than that...
polyphony is just more than one voice going on. homophony is one voice, like gregorian chant. homophony is all the voices moving together. its a kind of polyphony,because the voices are singing different notes but they are moving together rhythmically.
so this is a polyphonic texture
http://www.youtube.com/watch?v=y_vEuRykohM
this is monophonic
http://www.youtube.com/watch?v=kRLIz897DzY
and homophonic
http://www.youtube.com/watch?v=08Hb0e9cIS0
a fugue is kind of difficult. but basically there is a theme that is played then it is played in another voice usually in the dominant, i think, while the first voice plays something else. once it goes through all the voices that are in that fugue then the exposition is over and it develops the theme by inverting it and playing different episodic motivs.
that might have somewhat made sense, or be as the brits would say complete and utter shite.
if i were in israel i could explain it better because i would have my notes with me.
if you are interested in harmony than aldwell and scahcter's book "harmony and voice leading" is generally considered the bible of harmony to some.
and i think adwell also wrote a book on counterpoint.
i havent read the music theory for dummies, but it probably explains things better than i do.