The best place for a starter to live is in a glass jar that is large enough (1 gal) and has a non-sealing glass lid. Make sure your jar is clean and well dried.
250 g lukewarm water (to get started, you are likely best to use filtered water)
250 all-purpose flour
Mix well, using a ladle or Dutch whisk and let sit on the counter (at room temperature) for 3-5 days.
It will start to bubble and smell like it is fermenting. (This is good!!)
Remove more than of the starter and ‘feed’ it with equal parts flour and lukewarm water.