I am beginning to bake from Jeffrey Hamelman's book Bread, have had two wonderful successes, but am terribly confused on how to come up with 2 tablespoons of mature culture required for the Whole-Wheat Levain as described on p 168.

1. I don't have to buy the mature culture, right?
2. I need to make the mature culture, right?
3. Am I supposed to use the instructions in the appendix of the book and then incorporate 2 tablespoons of it?
4. Is a mature culture different from a sourdough culture?
   

As I scoured the book going from section to section I simply could not figure out what it is that I am supposed to do in order to make this bread. My frustration partly means I'm learning, which is exciting, but I'm also frustrated.

 Could someone please help me (and reference the book if possible)?

 Kind regards,

AW