General Units
Spearman

Quick to produce unit with low armour. Good for getting large numbers of men out onto the battlefield. Also useful for charging at ranged attackers and human shield tactics.
Can be countered fairly easily with tougher units e.g swordsmen.
Swordsman

More armour and a more powerful attack make these tougher units that the spearman, but at the cost of a slower preparation time. A single swordsman can usually take out more than 1 enemy spearman. Their strong armour makes them good units in most situations.
Can be counterd by tougher units or by a greater number of swordsmen.
Archer

Standard ranged unit. Archers can attack units that are still at great distances away and are brilliant for taking out low armoured units like halberdiers. Especially useful in large numbers and as support units. Place archers behind melee units to assist them.
Archers have low armour so can be countered by units that can reach them quickly before they have inflicted too much damage. Another tip is to let them get tnear to your side of the map before tackling them as then your units wont have to cover so much ground.
Halberdier

Slow moving, low armoured, but with a powerful attack. The halberdiers are very useful in certain scenarios. Because of their reach a single halberdier can kill a swordsman (sometimes) before the swordsman can inflict much damage. Halberdiers are particularly useful in groups of 3 or more against mounted units.
Can be countered very effectivley by ranged attackers e.g archers.
Axeman

Fairly tough, close range units. The axemen will keep charging forward while attacking, making them useful for driving the enemy back, which can help you get more men out onto the battlefield. Because of their offensive nature, they can also be useful against long reaching weapons like halberds.
Scout

Lightweight, fast moving units. Will nearly always be killed when involved in combat, but can be very useful for running through gaps in the enemy defence. Can be a life saver in the last minute of the game, when they can just tip the balance.
Longswordsman

Extra tough swordsmen. They have 2 attacks, a fairly quick swipe and a slower more powerul attack. Useful when you just need a bit of extra muscle.
Mounted Spearman

Fast moving, tough unit. Very useful in charges. Good at driving the enemy back while inflicting damage. Vunerable to clusters of enemies, particularly halberdier and longswordsmen.
Mounted Halberdier

Faster preparation time, faster movement speed, and more damage per strike than the spearman, but with lower armour, and slower attack speed.
Can be countered by groups of halberdiers and longswordsmen.
Mage

Powerful ranged unit with low armour. Their powerful attack can take out loads of halberdiers and other low armoured units. Because of their low armour, its often a good idea to put them behind a tougher unit liek a swordsman.
Can be countered by longer ranged units e.g by archers shooting them before they can get within range.