There are three types of Magic in Dark Souls – Black Magic in the form of Sorceries, Fire Magic in the form of Pyromancies, and White Magic in the form of Miracles. Do note that Miracles are affected by the resonance.
If you a player uses a miracle in their World Ex. Say Wrath of God, other players connected to the same network will see a resonance marker, and they can increase its power by using the same miracle themselves. It will resonate with the existing effect of the miracle and increase the power of the magic.