Theory is just a way for us to discuss music. Knowing the names of these Intervals and what they represent can really help when you start reading a theory book or need to explain a situation.
Intervals are the musical distance between notes, measured by half and whole steps.
Minor 2nd = 1 Half Steps
Major 2nd = 2 Half Steps
Minor 3rd = 3 Half Steps
Major 3rd = 4 Half Steps
Perfect 4th = 5 Half Steps
Diminished 5th = 6 Half Steps
Perfect 5th = 7 Half Steps
Minor 6th = 8 Half Steps
Major 6th = 9 Half Steps
Minor 7th = 10 Half Steps
Major 7th = 11 Half Steps
Perfect Octave = 12 Half Steps