Section 1--History of "tonal" music
Centuries ago, music was primarily composed to be background sounds for rich people's parties. Muscians tried the best they could to make their music interesting to themselves and worth creating, but never tried anything overly emotional, because at that time music wasn't made for emotion; if you wrote an overly emotional piece you couldn't make a living off it.
Still, music was an interesting, mysterious thing...Nobody knew why our species was able to make sounds that worked together and influenced the way we felt at the moment, or how certain rhythms just made us want to move. That's why philosophers such as Pythagoras started to create systems around which music works and studied acoustics (the physical science of sound).
The different cultures of the world begun creating different systems of scales and melody-creation. The Indians created a particularly interesting system of "ragas." The Chinese had some strange sorts of pentatonic scales. The greeks created a Western "modal" system of composing melodies.
Music at the time was one melody on one instrument, or several instruments playing the exact same thing, until in Europe around the 9th century, when composers began to experiment with "organum" by ading another voice (meaning another instrument or singer) which would typically be a perfect 4th or 5th away from the original voice. So if the song was C, E, D, C then the new voice may be G, B, A, G, or F, A, G, F.
Organum: When two or more musical voices are hamonized so that the melodic intervals of each are the same.
A melodic interval is when you play a note and then a different note, the inteval in between is melodic. A harmonic interval is the interval betwen two notes played at the same time. Skim through this wiki article on organum: http://en.wikipedia.org/wiki/Organum
Later, composers began experimenting with "counterpoint." Counterpoint is a method of writing multiple independent meldies to be heard simultaneously. This results in "polyphony," music with multiple independent voices.
Monophony: One voice
Homophony: One melodic voice accompanied by chords created by the other voices
This all may be difficult to understand at the moment, but it should all make sense as you continue your studies of theory.
Modal counterpoint was taken to the extreme by 16th century composers like Palestrina and was studied intensely by theorists like Zarlino.
Counterpoint of this era can be understood thoroughly through the following books:
http://www.amazon.com/Study-Counterpoint-Johann-Joseph-Parnassum/dp/0393002772/ref=sr_1_1?ie=UTF8&qid=1332626290&sr=8-1 This one was written in 1725 and is THE text on counterpoint, studied by Beethoven and Mozart.
You may be able to find some of these free to download online ;) Google is a wonderful tool.
In the late 17th century and early 18th century, composers such as Bach and theorists such as Rameau began to abandon the "modal" way of thinking and did things "tonally." This meant that instead of using scales or modes as the only way of making or studying music, the modes were limited to Ionian (major scale) and Aeolian (natural minor scale) and musicians could now experiment with tricks such as changing keys frequently or using chords "barowed" from different keys. Here is a site where you can learn all about tonal music:
Here is a place to get acquainted with Bach and other composers: http://www.getintoclassical.com/composers/bach/
And here is the wiki article on tonality: http://en.wikipedia.org/wiki/Tonality (the section "history and theory" mentions the books that defined tonality, which I recommend checking out, especially Rameau's "Treatise on Harmony")
How does this apply to your music today? Well the Grateful Dead bassist Phil Lesh used counterpoint to create his highly melodic basslines. Almost all country, blues, jazz, rock, funk, and pop music is made through tonal or neo-tonal methods of harmony.
Now for the happy ending. In the first paragragh I mentioned that music couldn't be made too emotional in classical times. Well fortunately for us Beethoven came along and ended the classical era and began the romantic era, where not only music, but all art became explicitly emotional.
This development led to musician's making music for music, not as background sound for the upper class. Composers such as Schoenberg even began experimenting with post-tonal, often highly dissonant ideas.
Centric: music with a pitch center (meaning almost all music, and efinitely all good sounding music)
Modal: a type of centric music theory using primarily scales as a means of composing melody
Tonal: a type of centric music theory which is much less limitting than modality, primarily used from the time of Bach up to the 20th century
Post-tonal: a broad term describing non-tonal music which is usually centric; experimented with by 20th century composers
Neo-tonal: a form of tonality used by modern musicians such as The Beatles, in which tonal methods are primarily used, but with some strange new techniques added
If you are interested in learning about music history: http://www.ipl.org/div/mushist/
Section 2--Introduction to counterpoint
https://www.youtube.com/watch?v=JcqrGLvs95M I highly suggest watching this series of videos on counterpoint. I'll begin to talk more about this technique in later lessons.
Section 3--Functional harmony
This is a very accurate article describing everything you need to know about the subject.
Section 4--The natural minor scale
Play the Cmajor scale. Now play it again starting on the 6th degree, A. This is the Aminor scale. Neat trick, right? Works in every key. So if you need to figure out the chords in a minor key, just move around the roman numeral pattern.
I-ii-iii-IV-V-vi-vii0 becomes vi-vii0-I-ii-iii-IV-V and you renumber it so it becomes i-ii0-III-iv-v-VI-VII
I don't expect you to have read every article I linked to by the next lesson, they are just there if you are interested. However, the youtube counterpoint series and tonalityguide.com lesons I will begin talking about eventually (before lesson 10 most likely), so by then you must those complete.