PlanetSide 2 Mission System will automatically assign objectives to players. You can see your current objective above the minimap, and an exclamation mark will point you towards the objective.
You get a small bonus to Experience Points for following the mission.
Mission System was added after the game’s release, and it was never properly finished. It’s supposed to help players navigate the world and get a sense of accomplishment, but effectively it is just an an automatically updating waypoint.
You should not pay any attention to the Mission System, and you can even disable its interface elements in the Interface Settings.