You got the attention of none other than our Instructor Chris Schlegel, who is the best qualified person, to explain to you and in the most simple language one of the confusing and mind-boggling sections in GT F#2 --- Intervals!!!
Now, you're ready to tackle that section head on! And if you can't still get a 100% clear understanding after his excellent explanation, I don't know why, ha, ha, ha!!!
As always, good luck!!!