After 24 hours your mix is on its way to becoming a sourdough starter.
Take a look at it. Do you see small bubbles on the top and on the sides? If so, great. If not, do not fret. It is very common to not see anything even after the first few days.
Whether you see anything or not it is time to feed you starter. This is called a “refresh.” We want to add another 1 cup fresh flour and 1/2 cup water to the mixture.
You have the option here to remove some of the mixture from yesterday. You do not have to but some people start their starter in a smaller container where space is limited.
If you do remove some of the mixture you can throw it out or save it in a jar in your fridge as use it in making pancakes, waffles or another bread recipe. I will post some of my favorite uses in an upcoming post.
Cover and leave for another 24 hours.