For those who might not be familiar with intervals, we’ll start by reviewing the core concept. The term sounds kind of advanced, but an “interval” simply refers to the distance between two notes, while a harmonic interval is when you play two notes at the same time.
Take any number of great players and ask them what the process was like, and chances are slim that you'll get any two who will tell you the same story. However, I would say there's a process or structure to learning the instrument. Just like with piano, there are foundational aspects of the instrument that we need to understand, which we then build on and develop as time goes on.