An interval in music is when you play or sing two different notes one after the other. It's like jumping from one note to another on a musical staircase. Some intervals are small, like stepping on two close steps, while others are big, like jumping over lots of steps at once.
Each interval has a name, like a nickname for the way it sounds. For example, if you play the notes C and E at the same time, that's called a third interval. If you play the notes C and F at the same time, that's called a fourth interval.
Musicians use intervals to create melodies and harmonies. They can make happy, sad, or exciting sounds by choosing different intervals in their music. So, just like you have to know your ABCs to read words, musicians have to know intervals to create beautiful music.