Difesa
Knowing about defending commands of your hero makes it easier to defend your palace alone or with others. A clever aggressor should always inform himself know about their target's possibilities, too.
Normal
If you set the defence status of your hero to normal, your hero will only defend your own or allied palaces and heroes in the same valley. Palaces always have the defend mode normal. If an allied hero stands in your palace, your palace will join the battle, if your allied hero is under attack.
Area defence
With the status area defence, your hero will defend all allied palaces and heroes in the same area.
Valley defence
In the valley defence status your hero will defend everything standing in the same valley as him. It won't make a difference whether friend and enemy is being attacked, and even neutral creatures like sentinels (level 2 onwards) will be defended.