Though these breads use only the most basic of ingredients (only flour, water, salt, and only occasionally yeast), they are rather time-intensive. The starters themselves can take anywhere from 6 hours to 6 days, and once you add the starter to the dough, that can take another day in of itself just to rise.
But believe me, the effort is well worth it.
Mix together 1/2 tsp yeast with 1/2 cup room temperature water, and let sit for about 5-10 minutes until the yeast is dissolved. Add 3/4 cup flour and mix together with a wooden spoon - do not use metal!) until it forms elastic strands that pull away from the sides of the bowl. Cover the bowl tightly with plastic wrap and let sit until it has tripled in volume; about 6 hours or so. I have also let the starter rise for two days: it will deflate, and you must add more flour and let it sit for a couple hours until it foams up again. But doing this I found gave the bread even greater flavour and texture.
The piece of dough that was saved can be frozen for several months. I just save it until the next week when I need to make the next batch of bread. When you want to activate it, simply let it thaw, place in a bowl, and add the same amounts of water and flour as the first time you made the starter. It will take longer to rise at first (and will each successive time to use the next piece of dough as starter), until after several batches you may need to add a little more yeast. I find every three batches I have to add another 1/2 tsp yeast. Each batch will also have more and more of a rich taste (though not as strong as sourdough bread). Experiment, and let me know if you have any further questions!