starter question

Based on your starter sample, my guess is: 

Weigh your starter sample.

If starter is 20%, then: 

White flour (100%) is 5X the weight of the starter.

Water (60%)  is 3X the weight of the starter. 

Metropical,

Normally you have to "feed" a starter periodically. In this case, it sounds like the notes suggest maintaining a firm starter in one of two ways. You can maintain it as a white flour starter fed by taking 20 parts starter, 60 parts water, 100 parts white flour (by weight) every 12 hours at room temperature. Or, you can take 10 parts starter, 70 parts water, 50 parts white flour, 50 parts whole wheat flour every 12 hours at room temperature.

When you are maintaining the starter, you will tend to throw out the remaining old starter each time you feed.

For example, if you want to maintain 180 grams of new starter, you would take 20 grams of old starter, add 60 grams of water and 100 grams of flour and make a dough out of it, place it in a jar at room temperature. You would throw out the remaining 160 grams of old starter unless you want to use it to make bread. The new starter will rise, peak, and dip in the middle, if the temperature is warm enough and the starter is healthy. That should take 12 hours, and then it is time to feed again.

You can refrigerate your starter if you want to set it aside for a while and not have to maintain it every 12 hours. There are a number of threads on this site about maintaining starters where you can get more detailed information.

To use the starter to make bread, set aside 20 grams of starter to keep your starter going. You can then use the remaining 160 grams of starter to make sourdough bread.

A simple recipe might be something like

160 grams sourdough starter

1000 grams flour

650 grams water

22 grams salt.

Mix ingredients and knead. Allow to rise by double in about 6 hours. Form 2 loaves. Allow loaves to rise for about 2.5 more hours. Bake at about 425F for about 30-45 minutes.

Bill