Units

In Warcraft 2, humans and orcs have equivalant units. This means that although they have different names, and graphics, they both have an equal or similar role in what they do. In the more advanced sections of this strategy guide, I refrain from mentioning the equivalant units because it becomes unnecessary.

A unit consists of everything that you can build out of your buildings. They include peons/peasants, ships, ogres, mages, etc. Each unit you have costs you 1 food to support. That means the more units you have, the more farms you will need to support your army. Units are built using several different buildings. A barracks builds footman/grunts, archers/axethrowers, knights/ogres, and ballistas/catapults. A shipyard builds every type of ship. An inventor/alchemist builds flying machines/zeppelins and demolition squads/sappers. Mage Towers/Temples of the Damned build Mages and Death Knights respectively.

Units are built, by selecting the proper building, and then pressing the hotkey for that unit, or by left clicking the units icon. If you have the available resources and food requirements, then the unit will start production. Below are pictures of all of the human and orc units respectively.

Requirements
Each unit requires a specific building, or several buildings in order to be able to build them. The list of buildings needed is given below

Footman/Grunt - Barracks
Archer/Axethrower - Barracks, Lumber Mill
Knight/Ogre - Barracks, Lumber Mill, Blacksmith, Ogremound/Stables
Ballista/Catapult - Barracks, Lumber Mill, Blacksmith
Demolition Squad/Sapper - Gnomish Inventor/Alchemist
Flying Machine/Zeppelin - Gnomish Inventor/Alchemist, Lumber Mill
Mage/Death Knight - Mage Tower/Temple of the Damned
Griffon/Dragon - Griffon Aviary/Dragon Roost
Oil Tanker - Shipyard
Destroyer - Shipyard
Transport - Shipyard, Foundry
Battleship/Juggernaught - Shipyard, Foundry
Submarine/Giant Turtle - Shipyard, Gnomish Inventor/Alchemist

With this is mind, you can see how killing certain buildings would hurt the enemy more than others. For example, killing the ogre mound or stables, stops all of the enemies barracks from producing knights and ogres. This becomes very important in games when you have an opportunity to take out some of the enemies buildings.

Building Times
Each unit also has a training time, which is the amount of time from when you start training the unit, until it is complete. Different units have different training times (for example, a grunt finishes faster than an ogre). You can see the building time properties if you go into you War2 map editor, click on 'player, and then click on unit properties. Check out this this question I was asked. It goes into greater detail on how the building times for units work.

Strategy - Main | Back (Structures) | Top | Forward (food)