I have to preface this post by saying that making yogurt is not at all complicated, and if this makes it look like it might be, that's just because I like to take a lot of pictures. And complicate things.
This is my method for making yogurt using my Excalibur Dehydrator. You certainly don't need a dehydrator to make yogurt though, and I'll address other options later.
I made a quart of yogurt when I took these pictures. Sometimes I also make two quarts at a time. You can use regular milk from the grocery store. We drink skim, so that's what I use for yogurt, and it works fine. If you'd like it richer, just use a higher fat content milk. Do make sure that the milk is not ultra heat pastuerized. This is done a lot to organic milk, but some other milk UHP as well. It's a high heat processing that changes the milk to the point where the yogurt culture won't be able to grow in it.
Whisk in 1/2 a cup of dry milk powder for each quart of milk. This provides more protien and makes a thicker, less watery yogurt.
Bring this mixture to a boil, making sure to whisk often so the milk won't scald on the bottom of the pan.