In Fallout 76 you can take part in main questions or side quests but there will also be Public Events found all the world.
Public events will appear on the map as hexagonal icons and can be fast travelled to if you like for a small number of caps. When you get closer to the event you’ll then be able to agree to be a part of it.
As the name suggests, Public Events are available to everyone in the local area, not just your party or group which means there will usually be much bigger objective as the overall group size will be bigger.
Once the event has been successfully completed, all players who participated in the event will be rewarded caps, experience and some randomised loot.