In morning, mix flour and water together In jar large enough to allow mixture to double. Keep In warmest part of kitchen.
After 24 hours, discard 150 grams of starter.
Add 75 grams each of flour and water. Mix. Put lid back on. Keep In warmest part of the kitchen.
Repeat this twice a day for the next four to five days,
You can now assess if your starter is ready to bake. Take a tablespoon of the starter at its peak, (risen and bubbly) and drop into some warm water. If it floats, you can probably feel confident to bake. I like to build a starter for two full weeks, but you may not need to do that.