Units of infantry and cavalry commonly include a standard bearer who carries the unit's banner and a musician such as a hornblower or drummer. It is also usual for units to be led by a champion; an experienced and able warrior.
The champion, standard bearer and musician, often referred to collectively as the unit's 'command group', are placed in the front rank of the unit whenever possible. When a unit turns to face its side or rear, they are automatically rearranged in the new front rank.
As we shall see later, a unit can also be joined by a character, in which case these models are also arranged into the front rank alongside the champion, standard bearer and musician. Don't worry about this for now - the rules for characters are explained later.