Referring to the part in your fingers - you can discard it.
Some applications with drum brakes have adjustment windows in the backing plates through which to insert an adjusting "spoon." The part you are holding is a dust cover for said windows. GM adjustment windows are in the faces (or flanges) of the drums instead of the backing plates. Typically, there is an oval knockout in the face of each drum that can be dislodged with a hammer and 1/4" punch. You can cover the resulting windows if you prefer, but it is unnecessary and rare for anyone to bother. Generally, the covers should be used only in applications that adjust through backing plate windows.