Yeast is a one-celled organism that provides the leavening (rise) to breads. It is usually sold dry, in small granules, and must be activated with water and heat. Yeast is also used to ferment wine and beer: it consumes sugar, and produces alcohol as a byproduct.
I'm trying to start my first "successful" sourdough starter. I posted a question about getting it started here:
Since I asked that question, I started a second starter according to ...