Here are the samples of AreaHook for some known Prison/Mine plugins.
To register your AreaHook, you need to implement the IAreaHook interface and register it in the onEnable() method of your plugin.
import com.vk2gpz.autosell.area.IAreaHook;
import com.vk2gpz.autosell.IAutoSell;
...
if (Bukkit.getPluginManager().getPlugin("AutoSell")) {
IAreaHook myHook = new MyAreaHook();
IAutoSell.getInstance().setAreaHook(myHook);
}