Disjuction introduction is a logical rule of inference that says that if P is true, then P v Q is true as well. In essence, it allows you to take true statements and tack on other random statements (regardless of their truth value) using the OR operator.
Disjunction introduction also allows you to use P to conclude Q v P. Once more, though, your professor may require you to place the new sentence to the right of the disjunction. Check with him or her to be certain.
This is our last rule of inference. Next time, we will begin learning proofs and proof techniques.