Stir ingredients together and put in a covered jar (quart mason jar to start). I use a metal table knife to stir.
Feed 2x a day till bubbly and ready for use--it should double in size. I use tape to mark where it was when I stirred so I can see it rise. One feeding a day will do in an ideal environment, however, it make take longer to bubble. Feed 2x daily until you see it double in size; also the day before baking with it for best rise results.
With each feed, you have a choice:
To keep your starter the same size, you will DISCARD 1/2 cup of your starter with every feeding.
If you want to GROW your starter: See article notes on the purpose of discard. You do not need to discard, but you do need to keep equal proportions of your starter/flour/water blend, especially during the first week.
Store in fridge if not using. I like to take a small portion (about 1/4 cup) and freeze for future use in case you need to start over.
For the water: You can use tap water--I use filtered to keep it as pure as possible.
For the flour: I personally alternate my feedings with Einkorn wheat flour and white flour