Well, the fifth paragraph is basically dealing with music theory.
First of all, you should know that the gap between two notes is called an interval. You name these counting the gaps between two keys following each other.
You got two options counting, for example:
Start with a C to a D; from C to the black key next to it (either Csharp or Cflat) it is one semitone step, from the black key to D it is one semitone step,too - this equals one full tone (a full tone consists of two semitones and is usually counting by going from one white key to the next). Ok, now to D-Fsharp and Db to F.
If you start counting the semitones, you'll find that it's both times 4, so you have the same interval (a major 3rd, by the way). Since both intervalls are the same, they sound the same, too (besides the fact that D-Fsharp is a little higher).
You should get yourself a book for beginners in music theory - it'll do you good, since theory knowledge often makes playing easier.
Ok, I don't know if I explained that understandably, but I do -at least - hope so :-)
Good luck with that piece.
Regards,