This rule is sometimes also referred to as _Constructive Dilemma_. This can be a bit tricky to understand because the goal is to derive or _introduce_ a new proposition separate from the disjunction you start out with. This may be disjunction, a single proposition or a proposition containing any other logical connective. You do this by constructing two sub-proofs, one for each of the disjuncts comprising the disjunction you start out with. If you can derive your target proposition as the conclusion of each subproof then you may invoke the conclusion in the main proof and take it to be derived.
