Hello. I've been making my own yogurt using the same starter culture for over 4 years. (my mother once had a starter for something like 15 years!)
Most people make it more complicated than it needs to be....
1. 1 gallon organic whole milk
2. pour in 2+ gallon stock pot and heat on stove
3. as milk gets hotter, slowly decrease heat setting on stove
4. bring to simmer/boil (milk will foam and rise...you want to maintain this for several minutes then it will collapse --->this
is when you turn off heat and wait)
5. wait --->when milk is about 100-110 degrees ladle about 4 ladles full into a bowl
6. add about 4-5 table spoons of starter yogurt culture (buy good quality or get some from a friend)
7. stir for about 10 seconds
8. stir stock pot of milk and add milk/yogurt starter culture back into pot
9. stir completely for 10 seconds.
10. pour into mason jars and place lids
11. keep warm for 6-8 hours (I put all mason jars into a roasting pan with lid and fill with warm-hot water, then wrap in 2 bath towels)
12. put in fridge.
not a lot of exact science. do it a few times and you'll see that it's pretty easy.