Mix 25 g water and 25 g flour together. Cover with paper towel and let sit for 24 hours.
To the same jar, add 50 g flour and 50 g water. This is a 1:1:1 ratio. Mix, cover and let sit for 24 hours.
To the same jar, add 150 g flour and 150 g water. This is a 1:1:1 ratio. Mix, cover and let sit for 24 hours.
From now on you will discard everyday. To a NEW clean jar add 50 g starter, 100 g flour, 100 g water. This is a 1:2:2 ratio. Mix, cover and let sit for 24 hours.
Repeat the step for day 4. This can be scaled up to make as much starter as you need, for example 200 g starter, 400 g flour, 400 g water.
After about 12-14 days your starter will be mature enough to make bread!
