Vault 76 is a place we could hear about already in Fallout 3 and Fallout 4, but only in Fallout 76, we can see it in full splendor. This is where the online part begins. In Vault 76, you will create your character, learn the basic mechanics of the game and get a Pip-Boy. However, you will not stay there for too long, so it is worth answering the question - can you return to the vault?
Unfortunately, after leaving Vault 76 you cannot get back to it. However, you can teleport right at the door for free - although you won't get inside, free teleportation can be useful for visiting nearby areas. For example, not far from Vault 76, there is a location where you will find the Power Armor. For more info, head to the "How to get Power Armor?" chapter.