Just mix some flour and water into a gluelike paste and set it in a bowl on top of the fridge.
Wild yeast, bacteria, etc. will come by, innoculate the "starter," and give you the means to rise bread, pancakes, etc. It's how the old timers did it--back in the day, bread always had a sour flavor from the lactobacillus (what gives yogurt and sourdough its tang.)