My sourdough starter: Freshly fed and happily active.
This is a natural starter. I mixed 1 part unbleached bread flour to 1 part warm water and left it in a warm spot for about a week (after the first 2 days I covered it with clear film). Wild yeasts from the air will start to activate the dough over time. This can take anywhere from 1 to 10 days. Every 12 hours the starter should be 'fed.' Remove one cup of starter from the bowl to throw away (while doing this, skim any gunk from the top as well). Then add 1/2 a cup of flour and 1/2 a cup of warm water and mix. By feeding the starter two things are accomplished. First, it keeps the starter active because the yeast has something to eat. Secondly, feeding the starter encourages the yeast to be active and discourages bad bacterias from taking over and eating the yeast. (More scientific accounts can be found if you google sourdough). Once the starter looks healthy (doesn't smell off, is a good creamy color) and active transfer to a jar and store in the refridgerator. Feed at least every two days in the same manner.
I will be making sourdough bread soon, check back.
A fantastic resource for learning how to make your own sourdough starter and bread can be found here on the eGullet forums. (You can also order starter here if you are not prepared to make your own.)