You do not need a special massage product. The main requirement is slip: a layer of facial oil, serum, gel or cream that lets the shungite stone move smoothly across the skin. Without slip, the tool can pull at the skin, which is uncomfortable and can irritate. If your usual moisturiser is rich enough and stays on the skin for a minute or two, you can use it directly. Many people prefer a facial oil or a few drops of serum because it creates a light, lasting glide.
If you use a product that dries quickly, apply a little more or reapply before starting the massage. You can also mix a drop or two of facial oil into your moisturiser. The amount should be enough to keep the skin damp and lubricated for the whole session, but not so much that the stone slides uncontrollably. Work in small sections: apply product to one area, massage it, then move to the next.
After using the tool, you can leave the remaining oil or serum on the skin or gently pat it in. There is no need to rinse, unless the product instructions say otherwise. If your skin is reactive, do a patch test with any new oil or serum first, and skip gua sha on areas that are broken out, sunburnt or otherwise irritated.