Units:
Player can research and train units. Both of those actions require resources and free villagers. If a player has units, he can defend himself, send support to other players or attack their settlements. Special units have aditional abilities, like spies (espionage) or counts (take over other players` settlements).
Here is the list of all units:
Crusader
Spearman
Barbarian
Bowman
Spy
Light cavalry
Heavy cavalry
Battering ram
Trebuchet
Count

Research:
Before training a unit, he has to be researched. To do so, a player has to have enough resources and meet the requirements for that unit. Reasearch takes time. Count is an exception - he cannot be trained in barracks.

Training:
Those units that have been already researched can be simply trained at the barracks. Every unit has a certain cost and time to train. The training time decreases as you upgrade barracks` level.

Retirement:
You can always retire your units and get back free villagers, but you will not get back the resources.

Conquering:
To conquer a settlemen you will have to reduce it`s conquer points to 0. After conquering other player`s settlement, you will have it for as long as you can protect it from other players.
If a count survives the battle, it can lower the conquer points between a range of 2250 to 2750. Right after that settlement`s conquer points drop to 0, it becomes a property of that player who gets to reduce it to 0.
To be able to train a count, you will have to build a residence of level 10, goldsmith of level 5 and buy golden armor. You can only conquer other players` settlements if he has more than 1 of them.