Librarian-how many powers each GAME turn

[usa_supersonic]

So in the codex(BA codex also) it says: " He can only use one power EACH PLAYER TURN"

How do you do it? for example turn 1 : (my turn) I use smite. And the my opponents turn 1 I get assaulted and use Might of ancients?
I have used one power each player turn

Or I am allowed only one power per GAME turn so if I want to use might of ancients... I do not use anything else in my turn...and can use the power in the opponents turn

NOte in the RULE book page 9: "In a complete game turn both players get a player turn"

And I can use one power each player turn....

I would say I can use them both in turn 1 for example