Choose a rival to fight. In the battle screen, swap any of the sigils under your portrait with those on the grid to try to match 3 or more sigils of the same type. Match the sigils of your demons to try to summon them. Once they are summoned, pay attention to the number of sigils floating just below the demons' health bar. This number indicates the minimum sigils of that type that you need to match to launch an attack. Defeat your enemies to learn how to summon their demons.