First, you figure out how big you want it. I measured across my stomach to figure out how big I wanted it. I'll use it for cramps and backaches. I doubled the material and then folded it in half. I sewed up each side and a few inches across the top on both sides.
You're done! You now have an easy to make heating pad! Just pop it in the microwave for a couple of minutes when you are ready to use it! You can also heat it slowly in the oven. Here are directions for that, takes 15 minutes: http://www.ehow.com/how_7795612_bake-heat-pads.html .