Katherine,
I would suggest getting it from the horses mouth, ie. talking with a
farrier who actually, makes, forms, and shoes horses. He will be able
to provide you with some basic understanding of what horseshoes do
beyond the obvious. He or she will be able to explain all the types
of shoes that are used and their purposes. Some are actually made to
correct problems in a horses gait, and some are made to do the same
while leaving no indication of this purpose in their hoof prints when
being sold.
Best of luck,
Tom