Hi Doreen! MSM is a supplement, just like Vit B or whatever. :) You can get it at any health food store. They often pair it with glucosamine for tissue repair.
MSM is a type of Sulphur, a compound which is found in every tissue. Usually we get enough of it in our diets, but it can help the liver and tissues to have some easily available.
Because the liver does so much detoxing of metals and hormones and what-not, it needs lots of different nutrients to break things down and expel the remains. Most of the B vitamins aid the liver in this action, as does MSM. So for a complete liver cleanse, it helps to take MSM for a week to make sure the liver can do all it needs to do.