You'll unlock the first 3 VR Missions during Episode 1, and the rest you will unlock as you progress throughout the story.
VR Missions can either be done Solo or Cooperatively online with 1-2 other players.
Depending on the amount of players you play with determines the requirements for the Medals.
There are a total of 32 VR Mission unlockable via story progression and various more via download.
You can earn a total of 96 medals (3 per mission) from the standard 32 unlockable missions.