First of all, I’m not a music teacher.  Nor am I offering some sort of magic formula.  Over time, many people have said to me that they’ve never bothered learning music theory because it’s too complicated or technical.  I’ve certainly read my fair share of books and articles that overcomplicated things, maybe it was an ego trip for the author.
So what I want to do is present information in an approachable way that should make sense and enable you to learn and apply music theory for future use.  I’ll start with the basics and provide a series of posts on a range of subjects to help build up to more detailed information over time.

To recap an earlier blog post, there are 12 notes in an octave.  These are shown on the photo of a keyboard below.  The octave starts with C then C#, D, D#, E, F, F#, G, G#, A, A# and B.  The next note will be C again but at double the starting pitch so we say it is the next octave.
When making music you can of course use any of these notes in any octave in anyway you see fit. However, we need to arrange them in certain ways if we want to sound musical.
We do this using Keys.  They can be major or minor.  The easiest way to think of them is major = happy and minor = sad.  For now we’ll focus on major Keys.
I’ve said before that intervals are the secret to music.  Major Keys have the intervals of tone, tone, semitone, tone, tone, tone, semitone.  If we take the Key of C this gives us C D E F G A B C (this C is an octave higher than the starting note.)
keyboard
This can be seen on the photo of the keyboard above.  I will cover intervals in more detail in a subsequent post.  For now, you just need to understand a semitone and tone interval.
You might have noticed that the Key of C major comprises of all of the white keys.  We could work out the major Key for any of the other notes in the octave but there are patterns called the circle of fourths and circle of fifths that move through the Keys in a structured way and again this will be the subject of a future post.
Back to the C major scale.  Each of these notes can represent the root note of a chord, which is basically a group of notes based on specific intervals.  We tend to use roman numerals to represent these chords as follows:  I ii iii IV V vi vii   Capital roman numerals are major chords and lower case roman numerals are minor chords, although the vii chord is a special case called a diminished chord.
So in the Key of C major you have the following chords: C Major, D minor, E minor, F major, G major, A minor and B diminished.
In order to explain chords in more detail, I first need to discuss intervals.  It would also be helpful to discuss the circle of fourths / fifths to show all of the Keys.  There’s quite a lot to take in already so I’ll leave these as topics for future posts.