No matter which side of the country you're experiencing Star Wars: Galaxy's Edge on, you should know how opening day and the subsequent weeks and months are going to work. At Disneyland, starting May 31 (opening day) through June 23, 2019, all guests wanting to enter Star Wars: Galaxy's Edge will need a no-cost reservation. Guests staying at a Disneyland Resort hotel will automatically get a time to enter Galaxy's Edge during their stay. Reservations opened on May 2.
At Walt Disney World there has been no announcement about a reservation system being put in place. Based on past opening-day experiences, you probably won't need one and will instead want to plan your day around the park opening and closing hours.