The word “interval” means distance, and we measure distance in music with a number. There are various ways to do this, but the easiest is to always start with major scales and number them: 1 2 3 4 5 6 7 8, and so on. Then the number tells you have far any note is from a lower note. As you may have guessed, there is a LOT more to this, but we will start with this simple idea first.