Here is roughly what I did. I found a "recipe" where the person making it did not mention specific temperatures (I liked this because of my lack of thermometer) and then made it how I was taught. This might seem complicated at first, but once you do it you'll see its really quite simple.
You'll need organic milk and organic yogurt with active cultures to start - I used Fage Greek yogurt, because I wanted strong cultures, but you can use any plain yogurt, really.
1. Heat the milk until almost boiling point. Watch out! As you know the milk will boil over. So at the point of boiling, when you see the milk start rising and eager to mess up your stove, TURN THE HEAT OFF! (Where I messed up...) Officially, the temperature should be 185 degrees.
2. Let it cool down but you want to work with it warm. So stick your finger in and if you can tolerate it for 10 seconds while still feeling the warmth, you're good to go. AKA: 110 degrees.
3. Mix in about 1/4 cup of yogurt cultures (the Greek one I mentioned).
4. Pour into mason jars, cover, and keep at 110 degrees for 6-24 hours. The longer you let it sit the less casein and milk sugar remains; at home we keep it in a dehydrator set at 110 for 24 hours. But I believe it is considered yogurt after about 6 hours, if you really want to cut it short. For me, I kept it at 110 for 12 hours (like I mentioned above), setting the jars in a covered container of water and wrapping it with a beach towel. I checked it every 1 1/2 hours or so, adding hot water as needed. It wasn't TOO big of a hassle, but it definitely made the hours of the day go by strangely fast...
5. After your desired amount of time as passed, place it in the refrigerator until chilled.
6. Enjoy! I like to add just cut up apples, but any other fruit/granola (if you tolerate grains) would taste great, I'm sure. Or even some vanilla, or some exotic things...the choices are endless.
(I am by no means a yogurt expert, but this is what has worked for me. There are many other little variations out there, some more complex/simple than others. Experiment and figure out what you like!)