How to barrel race beginner barrel racers?

okay so my friend and i are beginner barrel racers Ive seen barrel racing done many many times at my friends rodeo Ive always wanted to do barrel racing but it didn't totality stick until my friend said she wanted to do it to so we have both decided we want to do barrel racing but im not sure how to get my horse and her horse in shape my friend has a 14 year old paint and hes about 14.2 hands and i have an Arabian and she is 9 years old and shes 14.3 hands tall and i would also like to know how far apart are the barrels have to be any advice about barrels and getting are horses in shape would really help thanks much p.s. does your horse have to be a serten size to barrel race we do ride are horses often almost every day up to 3 hours