I got it from an organic market by my house called 'Roots'. Ive seen it in many different places though its pretty common. You want the slippery elm powder.
I mix a generous tablespoon with roughly a cup of distilled water, some prefer it thicker and use more. (Dr. schulze recommended 1 tablespoon per 3/4 cup). Mix it into the water slowly while stirring thoroughly with a fork, continue rigorously stirring until its a thick paste, it can be made hot or cold.