Not to not answer your question but check out
www.howtobrew.com and read chapter 14. It is pretty simple and well explained. In addition, if it is body and head retention that you are looking for a step mash might not be what you are looking for. With well modified malts, it is my understanding that a step mash may even thin your beer out instead of helping it. Try adding 1/2 lb of carapils malt to your mash for body and head retention. It has worked great for me. Also be sure to nail your target mash temp and don't let it get too low, that may cause a thin beer as well.