Blanch, if you have Safeway, you have commercial yeast - Fleischmann''s, SAF, Red Star, or ? Variously called active Dry Yeast, Rapid Rise Yeast,, etc. In foil or plastic packets.
Add the contents of a packet to a cup of water and a cup of flour, set aside for 3 days, and Voila! Sourdough Starter. Mix that with more flour and half a teaspoon of salt, and voila again; french sourdough bread (after baking, of course.)
If you want to keep your sourdough starter goig, it will need to be fed frwuently. I suggest doing a Google search for "soourdough starter", where you will find a plethora of advice on maintaining it.