You begin each of your turns with a certain number of available actions to give to your characters, called your action total. Your starting action total equals 1 for every 100 points of the game’s build total, and remains the same throughout the game. Immediately at the beginning of each of your turns, your action total becomes your starting action total.
Each time you give one of your characters a costed action you reduce your action total by one. When that total is zero, you can no longer give characters on your force any costed actions that turn. You do not have to use your full action total, but it does not carry over to your next turn.
The maximum number your starting action total can be is 10, regardless of build total.