“ATTACKS
Field Battle attack
With this attack you order your troops to fight only with the opponent's field army, without seiging the Fortress or pillaging. It is best used to destroy the enemy’s army on the field without risking a siege afterwards. This attack is rarely profitable on its own, but it can be very useful in the long run. The defending army is allowed to retreat if the option is turned on.
Pillage attack
Your troops put your opponent's peasants to flame. If a field army exists, your soldiers have to deal with it and then rob the Province. For every villager killed you get 5 gold,for every successful pillage you lose 4 honor.The defending army is allowed to retreat if the option is turned on.
Fortress Siege attack
Your troops have to overcome the enemy Fortress. If there is a field army, they have to destroy it and then attack the Fortress walls. The defending army is NOT allowed to retreat if the option is turned on. The field army of the defender always fights.”
try to read the manual:
http://www4.imperiaonline.org/forums/int/index.php?topic=26.0