summons question

[mindfray]

do summons with more levels/stars do more damage? or does it just increase the amount you can use them?

[Kawaii Ryûkishi]

It just increases the number of times you can use them in a single battle.

[Saber]

Your magic attack is what makes the summons do more damage. You can get magic sources in the underwater plane. Morth around until you get it.