That's some good stuff. I make it in a quart canning jar, just fill up the jar with whole milk, microwave (it needs to hit around 180 degrees, that takes 4 minutes in my microwave). Let it cool till it's lukewarm (around 95-100 def F), add in a spoonful of yogurt, stir, loosely cap, and stick it in the oven with the light on (my oven holds around 98 degrees). I let it set 12-16 hours because I like it firm you er and tangier.
If you use too much starter yogurt it can make it too thin, so if you have that problem don't worry, just add a little less next time and see if that fixes it.
If you have some that just stays thin and runny, no problem, you have cultured buttermilk! You can also mix a spoonful or two of yogurt into a cup of milk to make a buttermilk substitute.
If you let it sit till it's nice and tangy and drain off the whey you end up with a thick greek style yogurt. I use it instead of sour cream - similar taste, probably healthier.
If you want to try fermented pickles save the whey, you can add a little to your pickle jar to help jump-start the fermentation. It's lacto-fermentation (bacteria based) so it makes acetic acid, not alcohol, btw. Check out this blog for a start on fermented pickles (his politics may not be your cup of tea, but the guy knows good food): http://www.wildfermentation.com/fermentation-blog/