Don, yes, the cruise terminal is in downtown Honolulu. Waikiki is about five or so miles south and Hanauma Bay is another five miles further, or so, just past the community of Hawaii Kai. The best way to get there is to take a local bus (if you have no luggage) You can catch a bus to Waikiki by exiting the cruise terminal and then walking south (to the right) to the first bus stop. Buses are frequent and inexpensive.
Hanauma Bay is awesome snorkeling, but be aware, do not take any fish food, as feeding the fish is now prohibited.