I had a brick oven wood fired bakery when I lived back in VT, I made only sourdough (or naturally leavened) breads.
I made my own starter with only flour and water (Bleached is a no-no in either flour or water*!) let it sit for about 3-5 days stirring every day . . . it will get bubbly then act like it died . . . then it will get bubbly again, then take out half, and throw away, then feed it (half flour and half water) the first bubbly is the bacteria, the second bubbly is yeast!
Feed it every day for 3-5 days . . . then use it, I stored mine in the fridge, and would feed the morning of the day before I'd bake, leaving it on the counter, then mix up my first "chef" (a small amount which you would then add to, to make the final dough) around noon, (then put "Mikey" my starter in the fridge) in the evening just before bed I'd add more flour and water to the "chef", then the next morning I'd mix up the final dough, and hopefully have it in the oven around noon.
By stretching out the feeding (or "chef's") to make the final dough you do not allow it to become as sour tasting . . . you need to Knead the dough, it builds the gluten in the flour which traps CO2 gasses given off by the yeast, which causes it to rise!
*if you have chlorinated water, put it in an open container, and let it sit 24 hours, the chlorine will dissipate, and you can then use it, I used a filter!