With ribs, you'll often find a "silverskin" underneath the meat right by the back of the bone. This is a thin white membrane that will need to be trimmed and removed before you bake your ribs. If you do not do this then your ribs will turn out tough. carefully run a knife under the skin pull the skin up with your fingers and then discard it. Note that some ribs will come with the silverskin already removed and you could also ask meat counters at the grocery store to remove it on your behalf.