-The GUARDIAN GATES are the multi-colored icon on the map. Defeat the enemies surrounding each one to reclaim that gate. They are initially controlled by Nightmare enemies when you find them. Defeat all the enemies to relcaim that gate. There are 5 gates in each of the 5 realms. 25 total.
To view mission progress for each mission type:
Select World Board
Use to cycle through the different missions,
The number of missions by realm is at the bottom as you cycle through each mission type.
But again, all of these mission types can be located on your in-game map by pressing the button.