Music theory is built up of three different building blocks, these include harmony, melody and rhythm. Harmony is when multiple notes are played at the same time to produce a new sound. harmonies can also be used to create chords which often utilize the route, major or minor third and perfect fifth notes. A melody which is a combination of pitch and rhythm is like a tune which commences in a linear direction to the listener, melodies are usually what makes a song sound good or bad. Finally, rhythm is usually a pattern of chords that is repeated throughout the song, this can also be a strong foundation for the melody.
In music Theory there is an alphabet which only consists of seven letters, A to G. Each one of these notes has a different pitch. For example, on a keyboard they are only 12 notes but repeat upwards or downwards in octaves these 12 notes are, A, A#, Bb, B, C, C#, Db, D, D#, Eb, E, F, F#, Gb, G, G# and Ab. On a piano the white keys represent the natural notes that have no flats are sharps, Whereas the Black Keys represent the flat and sharp notes.
A musical interval is the distance between two different notes, in the musical scale there are 7 different intervals because you have two route notes. The smallest interval is known as a half step which is also 1 semitone, you also get a whole step interval which is 2 semitones, for example two semitones make a tone.