What it does, is allow you to fly with fellow simmers on line.
In “General Options” - “Data” ensure you have “OnLine Functionality” and “Multiplayer” turned on.
Then, when in the sim on the World Map Planner, look top right and find “Flight Conditions”.
In there, select one of the two options (your preference) in the Multiplayer section.
Once you have these options set, this linked thread will explain how to do the rest, although you may want to read it first!
There are a lot of ways to join others on line explained in this thread.