recipes out there for "catching" the wild yeast out of the air (think of it as good mold) or you can purchase a starter from several places. Your other choice is to get starter from someone you know. If you get a "pass-along" starter the donor will most likely give you instructions on how to feed (aka refresh) it. The instructions I got were something like this: every week use or pour off 1/2 your starter, then add 3/4 c sugar, 3 Tbsp potato flakes, 1 c warm water. I had never purchased instant potatoes before, so that part was interesting. But then after reading and learning about wild yeast starters, I learned I could really just feed it with flour and water. Once the micro flora get going in there, flour is the perfect food. I feed my starter usually once a week. I screw the lid on tightly and give it a good shake. Then I use what I need or pour some down the drain ("some" means I don't measure). I measure out about 1/2 c flour and 1 c of warm water. Again with the shaking and then unscrew the lid a little so the pressure doesn't build up. Then I store it (in a glass jar) in the fridge door until next week.
I do love http://sourdoughhome.com/ as a place to learn TONS about sourdough.
Starter can be used in any yeast recipe. A good rule of thumb for converting a store bought yeast recipe is 1 c of starter and replaces 1 packet of yeast (1/4 of an ounce) PLUS one cup of liquid.
I promise to share the most amazing sourdough pancake recipe soon.