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