It says that if P is true, then (P or Q) is true and so is (P or R), so the whole thing: [(P or Q) AND (P or R)] is true. But, if P is NOT true, then both Q and R have to be true so that (P or Q) will be true, (P or R) will be true and then the whole thing: [(P or Q) AND (P or R)] will be true.
