Now is the time to go face Gerhart.
Note: Defeating Gerhard will end the tutorial campaign. If you wish to do any exploring, or finish any remaining side quests, you should do it before fighting Gerhardt
You will most likely find Gerhardt in the Blackfang town on the far left of the map. This is going to be a tough battle so make sure to amass any units that are available in all your towns. Have your other heroes deliver the units to you if possible, or meet them half way. But remember, Gerhart's also gathering units so you don't want to wait too long before attacking him.
You should optimally be at least level 7 before confronting Gerhart, although it is ok to challenge him at level 5 if you have enough troops.
Do not worry too much about your healers at this fight. Gerhart will attack your healers at every opportunity and they will most likely die faster then you have a chance of resurrecting them
The key to this fight should be massive infantry. These have to break the siege gate and charge the other units in melee as soon as possible. Make sure to take advantage of your hero's move every turn, as every action counts in this battle.
At the beginning, while your melee units are destroying the siege gate, focus your ranged attackers on his healers, trying to do enough damage to kill the stacks faster then he can heal them. After that, focus on his ranged units such as the marksmen.
Hopefully, Gerhart will help you a little by sending some of his units out of the gate to attack your units. If he does, focus fire on any of those enemies that exits the gate.
Once you have broken down a portion of the wall of Gerhart's fort, send all your melee units charging in to finish off the remaining units inside
After beating Gerhard, a cutscene begins.
This ENDS the tutorial campaign and unlocks the main game campaigns:
Necropolis Campaign
Haven Campaign
Sanctuary Campaign
Inferno Campaign
Stronghold Campaign