Well, first you need sourdough starter. I have experimented, but not achieved anything to brag about by myself. So, I got my starter from my sister. Her directions came from here. The recipe below is also from there.
2 C of starter 3 C of unbleached flour (amount may vary) 2 TB of olive oil or softened margarine 4 tsp of sugar 2 tsp of salt
Mix all ingredients EXCEPT the flour. Knead in the flour 1/2 C at a time. Knead into a good, flexible bread dough. Let the dough rise until double in a large bowl. Punch the dough and knead a little. Form into a loaf and place on a baking sheet. Once the dough doubles again, bake at 350º for 30-45 minutes. Do not preheat the oven. The bread is done when the crust is brown and the bottom sounds hollow.
I am not perfect with the bread yet. I have tried a variety of shapes with the bread. No winner yet.