Questions about the game. (Endless Legend)

How to assign the army primary? After completing the quest they gave me an extra army of a pair of weak units and she somehow became the main, and the old on the sidelines.

And one more question - periodically I get a message that I can activate some kind of altar, activation of which were resources. What is the altar and how is it activated? (Upd. The altar figured out - I haven't seen icons)

Galina Evseeva
we need to build 4 altar of production, not knowledge

K0nsul
I have worked when built 4 altar production