Begin your journey to Strahnbrad by heading south. In the far southwest corner of the map you'll find a man with an exclaimation point on his head. Use Arthas to talk to him (right click) and they will join your army. Directly southeast of this man there is a woman who will give you your first optional quest of the game: She wants you to save her son Timmy.

Optional Quest: Save Timmy
Being the first quest of this kind this is very easy and you should accomplish the task with no loss of life. However, when you go into battle be sure to have the Arthas subgroup selected so his healing light spell is available to you. Use it on any of the soldiers that begins to get low on life. Use the 'T' hotkey to do this and left click the portrait of the soldier in need. The area where Timmy is being held is revealed on your map and there are no obstacles in your way. Use the aggressive move command ('A' then left click) on the center of the enemy formation and they will eliminate the kidnappers. Arthas can take a potion of healing here and after you've freed Timmy from the cage his mother will reward you with a ring of protection +1.

Back to the path for the main quest - look near the center of the map and you'll see the path you're to follow - we will encounter another optional quest - and one you should do: getting gerard's ledger back from the bandit lord.

Optional Quest: The Bandit Lord
This is easy like the Timmy quest although this time you will encounter almost twice as much resistance. You'll receive a potion of mana and the ledger upon defeat of the Bandit Lord (it's not hard just remember to have Arthas ready to heal anyone whose hit points are dropping rapidly say.. when they get around half?) and you will receive a Tome of Strength for your effort when you return the ledger to Gerard. Use the Tome of Strength on Arthas and it will permenantly improve his strength by +1. I also gained a level at the end of the battle here and I chose devotion aura as it improves the armor of all nearby friendly units. Very useful for keeping them alive. And with Arthas' healing ability they'll be pretty hard to take down.

Now for the final task. The main quest of the first chapter. We'll arrive at Strahnbrad by crossing the bridge and almost immediately encounter Orcish resistance. Two grunts are here to welcome you and they're seemingly more powerful than your average bandit. Heal any units that are really weak - remember you do have a potion of mana in case things get dangerous and you need to heal a unit. When you enter the town you'll see the Slave Master heading to the northwest. There are small pockets of orcish resistance around the town square here, I cleared it and managed to not lose a single unit. I didn't even come close.

You should then prepare for battle and head northwest where the slave master was heading. I used my mana potion and avoided any loss of life here although really it doesn't do you any good as it's the final battle of the mission. As long as Arthas is fine - and he should be- you'll finish off the slave master quite easily and move on to chapter two.