2 ticks are used every hour automatically as long as you have enough.
If you set your troop cap high then every hour those 2 ticks are converted into a troop and increases the size of your army.
If you are at your troop cap then you make a small amount of silver instead each hour.
You can change your troop cap here if you havent already done so:
http://c-rpg.net/index.php?page=strategusgeneralparty