SPF:
If you look
here at the Mission Index you will see the
Key at the top of the post.
If the mission is MP it goes in your
MP Missions folder, if it has the
Campaign tag then it goes in your
Campaigns folder. If it has no tag or has the
MEC tag then, like Cheetah said, it goes in your
Missions folder.
Hope this helps somewhat.
Rhys