There are many different kinds of clay.You will be mixing clays according to a recipe for the desired working properties. All clays have silica materials, alumina materials, and flexing agents which allow them to fuse and melt together in the kiln to become rigid. A simple stoneware clay has only a few ingredients.  A simple Internet search will pull up quite a few different recipes for you to experiment with.  The recipe you are using will be a simple stoneware.  It has some Cedar Heights gold arc clay in it, which is a raw clay, the ground silica,and a little bentonite because bentonite is a really sticky clay that helps to bind everything together and give it a little bit more plasticity in the end. All of these materials should be easily found in your local art supply store.