The number of streamers (one to five) on a company's banner graphically indicates its experience one streamer represents the lowest experience and five indicates the best. The more experience a company has, the more proficient in arms it becomes. Experience is gained through combat by destroying enemy troops. 'Experience' indicates the company's fighting ability.
The height of the tassel on the company's banner pole also indicates the current morale. If morale plummets too low (for example, through troop losses in combat), the company will flee. 'Morale' indicates how willing the company is to fight. Naturally, you may wish to wait until a fort has mustered enough troops to be effective, but nevertheless, as soon as soldiers appear, they're ready to go. As soon as at least one soldier appears in a fort's mustering yard, you're ready to begin giving orders. As stated above, each fort produces soldiers who comprise a 'company' that can be given orders as a single body.