I used Yogourmet starter. You can get it at Whole Foods or other health food store. Bring organic milk in double boiler to about 180 degrees for 8-10 minutes. Use a thermometer. Then quickly cool milk to about 105-118 degrees. Take a cup of milk and mix in starter and then mix with the rest of milk.
Line an icechest with aluminum foil and put hot water in a couple of jars to heat icechest. Put yogurt in a jar and place with water jars in icechest and cover with a dishtowel. Close and leave completely undisturbed (no moving chest during fermenting) for 20 hours or so. Then put yogurt in fridge.
I could give you more precise instructions but it's trial and error. After you make it for a while, your quality will go up. Google yogurt making. You can also get a yogurt maker.