J,S and L are vectors.
The J=0 level corresponds to a parallel orientation of L and S, where they point in opposite directions, because J = L + S so we must have S = +-L.
The J=1 level corresponds to a perpendicular orientation of L and S, because J = L + S so L or S must be 0 and the other +-1.
The J=2 level corresponds to a parallel orientation of L and S, where they point in the same direction, because J = L + S so we must have S = L.