Bethesda gives us Fallout 76 Teaser Trailer
Fallout 76 will have quests and a story. It will feature base-building, like we found in Fallout 4, and other survival-based and multiplayer mechanics, according to people over at Kotaku,” One source cautioned that the gameplay is rapidly changing, like it does in many online “service” games, but that’s the core outline.”
Vault 76 is already a part of the Fallout canon. Vault 76 was mentioned in Fallout 3 and Fallout 4. Vault 76 was meant to open 20 years after the nuclear war. Not much time for the crisis to settle so we cna assume things will be pretty tough and rough; nothing like the world of Fallout 3 and Fallout 4 which had cities and settlements and were set 200 years after the war.
There’s more info on Vault 76 at the Fallout Wikia here