The Happiest Place on Earth will start its reopening schedule from the 11th of July as the Magic Kingdom and Animal Kingdom parks welcome their first visitors post-COVID. EPCOT and Hollywood Studios will follow soon after on the 15th.
Note that no new tickets will yet be available for sale as the parks implement their first phase of reopening and reduced capacity programs.
All visitors will be expected to maintain a social distance of 6ft/2m from others outside their party, that means the parades and firework/light shows are on hold for now as they tend to attract a crowd. Likewise, character meets are off the table - Disney has suggested that their beloved characters will still be in the parks, however I'm unsure what that means at this time.
Expect increased hygiene measures and engagement related to hygiene measures from the Disney Team while on the grounds. That will most likely look like hand sanitizer stations popping up around the park and encouragement to wash your hands frequently during your visit.