In a glass container, mix the flour and water until well combined. The consistency should resemble a thick pancake batter.

Cover the container loosely with a cloth to allow air circulation. I prefer using a mason jar or weck jar and setting the lid on top. You want to capture yeast from the air, so if it's airtight, that process won't happen. The lid is primarily to keep dust and other particles out of the starter.

Stir the mixture well, ensuring there are no dry flour pockets.

Cover the container and let it sit at room temperature.

Ideally, feed once in the morning and once in the evening for best results. If you skip a feeding, that's ok, but you will decelerate progress if you leave it without feedings for too long (it gets hungry!)

Once you have seen your starter rise to double after feedings, consistently, it should be ready to use. You can also do the float test to see if it floats in water. If it does, it's good to go. Just scoop out a bit of starter and put it in a glass on water to test.