Intervals are always counted from the lower note to the higher one, with the lower note being counted as one.
Depending on the size, intervals can be: Unisons, Seconds, Thirds, Fourths, Fifths, Sixths, Sevenths...
Intervals can be described as Major , Minor, Perfect , Augmented, and Diminished.
When notes sound successively, it is a melodic interval. When they sound simultaneously,it is a harmonic interval.
Seconds, thirds, sixths and sevenths can be:
Fourths, fifths and octaves can be:
We recommend starting with these activities
Alice tone or semitone
Beethoven and Major Scales
If we add a half step to a Major or Perfect interval it becomes Augmented
If we rest a half step to a minor or Perfect interval it becomes diminished
If we rest a half step to a Major interval it becomes minor
If we add a half step to a minor interval it becomes Major
Let's take the example: C to A
lower two semitones
by adding a double flat
to the A
lower a semitone
by adding a flat
to the A
Just convert the A to A sharp
and you will have another semitone