You will want to "feed" your starter at the same time every day for the best results. Feeding just means you will be taking some old mixture out and replacing it with new mixture. This helps the yeast get stronger as you feed it fresh flour.
With a CLEAN spoon, give the old mixture a quick stir. You may notice the bubbles on top are a bit crusty. That's ok, just mix it well. Then scoop out 1/2 cup of the old starter.
Feed the starter with 1/2 cup flour, and 6 tbsp of filtered water. Stir it really well, wiping down the sides and making sure ALL the flour is mixed in.
On day 2, your starter MAY have a few bubbles in it, and it may have loads. It all depends on the temperature of your kitchen and the yeast that is floating in the atmosphere. As the days go on, you should see more and more bubbles as the starter becomes more active and happy. See Notes. Cover the bowl, and set aside until the next day/feeding.
Repeat this for Days 2-4.