Music interval is not difficult to learn. Let's start! First, I suppose you already know about CDEFGAB or Do Re Mi Fa Sol La Si. Let's assume that the notes are stairs. As you go up the stairs, the notes will get higher, right? When you step up from C to D, it is called 'whole step'. But actually there are more notes than that. You can also go up just a little bit, so in this case, you're going up from C to C#. This is called 'half step'. If I include all the notes(whole steps and half steps), it would be, C C# (aka Db) D D# E F F# G G# A A# B. So, when you step up to C# from C, the note is going up for 'half step', which is also called 'semitone'. Semitones are the smallest interval. And this semitones will be the standard for you to understand intervals.