Personal Navigators are the printed "newsletters" provided to passengers on a daily basis. Usually these are provided in your stateroom late at night (for the next day) or early in the morning. Navigators are also posted at Guest Services. They describe all of the ship's activities, including a schedule of the day's events, food service locations and hours, advertisements for deals (like the spa), desk contacts, dress codes, and other good stuff. It's the most useful document on the ship.
When you check in, they'll give you some preliminary information, including lunch service locations and Palo, spa, and excursion reservations. For Palo, it was Wavebands on the Wonder, Studio Sea (right above Lumiere's in the atrium) on the Magic. They have a board posted with the itinerary and separate lines based on each day, as well as a separate line for high tea and brunch reservations (for longer cruises). The maitre'd is also at the entrance to answer questions before you get in line. If you want to visit the spa/salon, they will take you on a tour and describe the services, after which you can make reservations. The excursion desk is off the atrium. Usually these are open for reservations until about 3:30, so people can prepare for the safety drill at 4.
After I made 3 Palo reservations, 3 spa/salon reservations, and 2 excursion bookings, then examined the Navigator and movie listings, I had to make up a separate calendar by day and time to keep everything straight!