There are lots of recipes you can look up, I dont use yeast.
1 cup all purpose flour (can also use whole wheat, rye, or a mix of all purpose and wheat or rye)
1 cup spring water or filtered water
Stir with a wooden spoon until mixed. Set on the counter at room temperature and cover with a clean cheese cloth or kitchen towel.
Exactly 24 hours after you made your sourdough starter recipe from scratch, remove half of the mixture from the bowl and set aside. This is your sourdough discard.
Then feed your sourdough starter recipe for bread by adding 1 cup of flour and 1 cup of spring water. Stir with a wooden spoon until combined. Cover with a towel and let sit at room temperature.
Every 24 hours, repeat the instructions from day 2. Remove half of the mixture and feed your sourdough starter recipe from scratch.
Continue to discard half and add a cup of flour and a cup of water every 12 hours.
DAY 7- Transfer your sourdough starter to an airtight container and place in the fridge. Feed it once a week to keep it going. You'll remove half of it each time you feed it.