Simply grate them up in the right proportions, mix and there you go. There have also been posts going a step further that explain how to make soap from easily purchased oils, meat counter fat or suet, commercial lye and fragrances. It's just not that hard if you make use of the ingredients and instructions easily found these days.

But what do you do in TEOTWAWKI if the stores close, either from lack of product to sell or from looting? What if the commercially made ingredients for so called "homemade" soaps become unavailable? You need to keep clean or you'll likely get sick. And you could certainly use some trade goods for barter...  and everybody needs soap.