Index -> Playing the Game -> Power Phase
In this first phase of each turn, players receive an amount of power they will have available during the turn. Each player receives 3 power, plus 1 power for each glyph beneath the hero player's characters.
It's Jason's turn, and there are two glyphs beneath his characters (from completing two missions on previous turns). Jason and his opponent Paul each receive 5 power to spend during this turn.
Power can't be saved from one turn to the next; anything you don't spend by the end of the turn is lost.