I'm definitely not an expert and I'm sure people will disagree, but this is what works for me:
to make the starter on day 1 just add a few tbsp plain flour and some water to a jar. i dont measure this but basically youre looking for a consistency where if you put some on a spoon and turn it over it takes around 3 seconds to drip
each day feed it a bit more with some more flour/water, looking for the same consistency
continue until your starter is bubbly and smells 'yeasty'. you may get a 'false rise' after a few days where it looks/smells like this, but it isn't ready yet. it probably won't be ready for 10-14 days ish
every night leave out with the lid loosely on. once your starter is 'active' you can start storing in the fridge with the lid tightly on when you aren't baking, and don't need to feed in this time.
when you're ready to bake i make my dough with 100g active starter, 330g water, 500g flour (strong white bread), 10g salt. mix, cover, leave for 30 min - an hour.
then do your first set of stretch and folds (stretch the dough up from one side then fold it back in then repeat from the next side). i like doing 20 for my first set. then cover again and leave for 30 min then do 4 stretch and folds. repeat the covering/leaving for 30 min/4 stretch and folds around 2-4 further times. then cover and leave for around 3-5 hours.
then you want to shape your dough into a ball and put in a proofing basket or if you don't have one a bowl and leave in fridge for around 8 hours or overnight.
when ready to bake preheat your oven with your dish inside (i use a le creuset dutch oven) at 230 degrees
once hot, put the dough in the dutch oven and score the top. bake with lid on for 30 min
then reduce heat to 200 degrees, bake for a further 20 min with lid off
LET COOL FOR A FEW HOURS BEFORE CUTTING OPEN
Sorry this was long! I used tiktok and reddit to learn how to make sourdough so would defo recommend. there's a girl on tiktok that teaches you how to make 'simple' sourdough which is where i started and i basically adapted it from there.