This is a real question? Easy means its easy for you. Hard means its a little less easy (this game does have AI that can only be described as French, after all), and Unfair means the computer is on hard but gets extra money.
If you look on your keyboard on the top right there should be a key that says "Pause". It pauses Sins. You can order units to attack and use abilities when paused, and when you unpause they will do as you commanded. Super useful.