You need to continue from your last saved game, and get check marks in all three of the first campaigns to be able to proceed to the next level of campaigns. If you start another campaign without loading your previous saved game, you will be, in effect, starting a new game. Units with secondary abilities. All of the units with secondary abilities work pretty much the same way. For this example, we'll use Archangels.
Archangels have the ability to resurrect dead allied units once per combat.
When it is an Archangel's turn, simply move the mouse pointer over a dead allied unit. The mouse pointer will turn to a spellbook icon. Click on the dead unit and it will be resurrected. Pit Lords - Resurrect dead allied units as Demons, once per combat. The number of raised units cannot be higher than the number of Pit Lords performing the resurrection.