Every army has a heroic character to command it. The General model is in command of the whole army and represents you personally. We refer to this character as the General, although this is only to distinguish him from other heroes. He might be an Orc chieftain, a Bretonnian Duke, etc. Some armies are commanded by the ruler of their entire nation. For example, the Emperor of the Empire and King of Bretonnia are mighty warriors who are ever-ready to ride out at the head of their forces.
The character with the highest Leadership value is the General of your army.
If several characters have the same (and highest) Ld value, choose one to be the General at the start of the battle and announce it to your opponent. The General is an important character, because he can inspire others to fight on where they might otherwise turn and flee.