I found a web site that specialized in cultures for making yogurt, sourdough, buttermilk, and a host of other things. Not only do they carry and sell the culture starters, but there are some videos and recipes as well. www.culturesforhealth.com
If you want to really make it easy on yourself in making some basic yogurt, get some plain (no flavor) yogurt from the store. Heat some milk (I used 4 cups) on the stove until there are bubbles forming around the edges. Let the milk cool to lukewarm (no more than 110 degrees F.) When it is cooled enough, add a couple of tablespoons yogurt to the milk and stir. If you have a yogurt maker, place the milk mixture into the container (s) and plug in. There is a way to make yogurt without a yogurt maker, but I have not done this yet, so I will not comment on it. Although I have made Piima yogurt (a culture from cows in Europe who feed on the Butterwort plant). That yogurt turns out like a drinkable texture. It has to be replenished every week, and it does not have to be made in a yogurt maker. It can sit on your counter for about 18 hours and finish.
Yogurt is a cultured food and is excellent for digestion. You can add fruit and flavorings after the yogurt is done, but save some of it to make the next batch of yogurt with.
Buttermilk is really cool to make. I almost couldn't justify ordering the culture because I don't have many uses for buttermilk. However, I have recently found a couple of recipes that use buttermilk, so I have been making it ever since. I do freeze some of it and defrost it as I need it, then always replenish it by making another batch.
The recipes at the site above are very interesting. They also have cheese recipes and a recipe for sour cream. Get on their mailing list for the latest updates too.