as far as the collection thing goes, just google dressage and read thru that and it'll explain collection and getting a horse on the bit, meaning in a frame.
With my gelding he didnt really have a butt and we worked on trotting for hours everywhere esp up and down hills. Soon u'r horses butt will be so big it'll look like an apple! Lol but that's a good thing.
"The horse you get off is not the same as the horse you got on; it is your job as a rider to ensure that as often as possible the change is for the better."