An interval is the distance between two musical pitches. It distinguishes whether the note is higher or lower than the first note and provides a means to measure and notate music. Intervals range from the first note above or below an original note upward to the octave of the original note. The octave represents the original or prime note repeated again after a full cycle to the eighth interval. For example the note A can be observed as another A one octave higher. A half or minor step is a note split in two, such as in the case of moving from A to B. One half step from A would be to A# and the second half step would be to B. To take a whole or major step you would simply move from A directly to B.
Intervals are the building blocks for scales. In a major scale each note is played to form the major scale by drawing out the interval distances between each musical note in the form of major whole steps. As noted, there are eight intervals between the original note and the octave. They are in order: prime, second, third, fourth, fifth, sixth, seventh and the octave. To form a major scale you must pick out the notes falling on the prime, and then follow with a major second, major third, fourth, fifth, and major sixth and major seventh interval notes. For example, in the major of E, you would begin with the note E and then count upward by intervals. This would begin the construction of the scale.
As in the case of the major scale, the minor scale also takes into account the prime, second, third, sixth and seventh interval notes. The only difference between the two is that you must return to the understanding of half and whole steps to position the minor scale in intervals one-half step lower than those in the major scale. You will count or move upward one half step instead of a whole step to create the intervals and scale. The minor scale is created by minor intervals. This means that for the former major second you will now have a minor second, minor third, and so on, for the scale.
Imagine that you have a C chromatic scale of all possible notes in the musical spectrum: C to C#/D- to D to D#/E- to E to F to F#/G- to G to G#/A- to A to A#/B- to B to C again. Note that the space between E and F and B and C has no sharp or minus versions, but to move from E to F and B to C is a whole step. If you are constructing a C-major scale using major intervals, the notes picked from this chromatic scale would be C, D, E, F, G, A, B and then C again as the octave. If you are constructing a C minus scale the difference is that you are using minor half step intervals at the second, third, sixth and seventh positions instead of major whole step intervals to construct the scale. The scale for a C minor now becomes: C , D, E-, F, G , A-, B- and C.