Per the Disney parks blog, Star Wars – Galaxy’s Edge is set to open at Disneyland on May 31st and Disney Hollywood Studios at Walt Disney World on August 29th. The new land will open in two phases with phase one opening with Millennium Falcon: Smugglers Run.
Star Wars: Rise of the Resistance will open on phase two which will be announced at a later date.
According to the Disney Parks blog if you are planning to visit Disneyland on opening day through June 23, 2019, you will need valid theme park admission and will be required to make a reservation (at no cost), subject to availability, to access the land. Information on how to make a reservation will be available at a later date.
However, at Walt Disney World, a reservation will not be offered. Valid theme park admission to Disney’s Hollywood Studios is required to visit Star Wars: Galaxy’s Edge after its opening on August 29, 2019. Capacity is limited. Additionally, Star Wars: Galaxy’s Edge will be open during Extra Magic Hours. During Extra Magic Hours guests staying at select Walt Disney World