Edit: Due to the rise in Covid cases Disneyland has delayed the reopening of the theme parks with no new date yet.
Disneyland is planning the reopening of its parks and resorts in phases beginning July 9th. The first to reopen will be Downtown Disney on July 9th, then both Disneyland park and California Adventure park will open on July 17th finally the 2 of the 3 resorts Paradise Pier and Grand Californian hotel will reopen on July 23.
Once the parks reopen they will require advanced reservations to enter the park to help limit the number of people in the parks. They are also not selling any new tickets at the moment to give those with cancelled vacations the first opportunity to enjoy the parks.