Let’s say you fed your starter 24 hours ago, and you’re just about to feed it again. This is when you want to bake with it. Take some starter out of the jar before you feed it, put in a bowl and follow one of these recipes. Then feed the rest of the remaining starter in the glass jar, putting a lid on it (or some cling wrap with a rubber band around it).
Why you do this is because you want your starter to be “hungry” when you bake with it. Take a look here to see how often, and with what flour/water ratio to feed your starter.