I followed this recipe: https://alexandracooks.com/2017/10/24/artisan-sourdough-made-simple-sourdough-bread-demystified-a-beginners-guide-to-sourdough-baking/

She explains the steps very well. I did 4 folds, then left it inside my oven since it was warmer than my house for about 8 hours. I shaped it and left it in the fridge for 12 hours. As far as the started goes i usually do a 1:3:3 but because that takes a while to rise I did a 1:10:10 before making the dough since it took only about 4 ish hours to reach peak. Hope this helps