Campaign Types are a new thing that we've been working on for quite a while, and originally Sage and I were designing these together back last May. Now that the game has returned from beta, Sage has put together a comprehensive video guide that explains the where, the why, and the how of these new modes.
The truly important information is also available in the game, of course -- Sage himself wrote a lot of the tips and explanations that are in there -- but sometimes there's nothing like a good video to really show things off.
Enjoy!