sidepulls are just bridles that dont have a bit. they work by exerting pressure on the horse's nose to get him to stop, turn, etc. you use them the same as you would a normal bridle w/ a bit, but the horse will respond more when you ask him to turn. thats pretty much all i know, im not very familiar with them as i ride tennessee walkers and they are almost always rode in bits with shanks. i hope i helped!
btw... neck reining wont work with sidepulls...i dont know if you're familiar with neck reining