How do you make probiotics?

Well actually you do not "make" probiotics at all. You cultivate them.

Probiotics are a living organism. They are a class of about 2,000 various bacteria that have been identified to be helpful to the human digestive tract.

You can purchase live cultures, or even better perform some research on the various species of probiotic labeled bacteria and purchase them in dried spore form. This is a great way to purchase them as in the spore state they generally have a shelf life of about 2 years, and are not activated until moisture source is added.