Everyone starts the same way , filled with doubt about making and maintaining a starter , the internet is filled with how to and how not to videos which if you watch enough of them will probably be put off forever.
I have found that precise measurements are not required , kick off with a wide necked jar or container , put equal amounts (300mls/g) of water and flour ( strong bread preferably) and mix. The texture you are aiming for is a stiff batter, leave the lid loose to enable air to react with the mixture , add a little water an flour daily for three days or so.
By the third day you should start to see bubbles appearing and detect a smell which can be off putting ! ... this is good !
Ignore the starter must double in size nonsense - once you have bubbles your starter is ready. You will need 150grams per loaf.
If you aren't baking for a couple of days you can let your starter rest in the fridge ( I put the lid on ) a day or so before you bake whip it out and feed it two or three times to wake it up.
Watch My Tutorial here :- https://youtu.be/OewbQiB8FW0?si=cWoflrJykeDslNIi

Only the crunch of a well done crust stands between you and the delightful texture of a crumb filled with just enough holes to hold that lightly salted butter that a loaf from JonDough deserves 8/10 *****

For 1 Loaf - 150G Starter - 500G Strong Flour - 250ml Tepid Water - 20g Salt - 25ml Olive Oil
A couple of large mixing bowls , Scraper or Spatula , Pie dish and Ovenproof Casserole Dish to cover Pie Dish , Banneton basket,Grease proof paper , Bread Lame or sharp knife , wire rack, cling film
Mix the flour and salt in one of the bowls - In the other mix starter , water and oil - bit by bit add the flour and salt mix
mix together ( I use the scraper ) once mixed leave to stand for 45 mins covered with cling film - then every half hour turn the dough from the edge into the middle for 20 seconds or so - do this three times - spray a little oil onto the cling film and leave for 12 hours ( I tend to mix in the evening ready for morning baker time) - Tip the dough onto a lightly floured surface , gently flatten it into a square ish shape and stretch from each edge to the middle a couple of times , shape into a ball and place in a flour coated banneton - leave for 30 min minimum a little more wont hurt- pre heat oven with dish and lid at 240c - tip dough onto a sheet of baking paper score or slash with Lame or Knife deep enough that you can see the softer innards - place in the pre heated dish and bake with the lid on for 30 mins - after 30mins remove the lid and lower the temp to 190c for approx. another 25mins - check after twenty to see if you are at the golden brown stage or test with a thermometer , centre temp should be 96c - remove from oven and cool on a wire rack. enjoy that smell
Sourdough is at its best on the first day , the fresh natural nature of the ingredients means that after day one toasting is recommended - store in an airtight container or bread bag if you have one , it will keep for 4 to 5 days but rarely survives that long in our house.
As I bake a couple of times a week I leave my starter on the worktop lid loosely on covered with a tea towel ( the most common owl in Britain ! ) you can store in the fridge with lid on and feed back to life a day or so before you intend to bake, you may also freeze a portion of a successful starter ( this acts as an insurance policy should you have any starter issues ) Your starter will improve with age and care .
There is lots online about discarding a portion of your starter and plenty of ideas for what to do with that discard , I bake two loaves twice a week and have never thrown any starter away , some says it improves strength, I prefer to be frugal !