A Channel is someone who can sense mage energy and funnel it, moving it from one place to another or from one or more mages to another, but cannot actually use it.
While lessons can help a Channel improve their technique, the ability to act as a channel is innate and cannot be taught. It operates at an almost instinctual level.
Karal acted as a Channel on three different occasions to halt the Mage Storms. The first time was at the convergence point where the Valdemar, Hardorn and Iftel borders meet. He accepted mage energy coming from Florian and Altra, combined it and converted it into a form An'desha could use, then fed it to An'desha to power the breakwater spell.
The second time, Karal used one of Urtho's remaining weapons. Though the weapon was designed to wreak destruction on both the physical plane as well as the magical one, Karal channeled all of its destructive force into a single magical explosion that acted to cancel out the incoming waves of the Mage Storms. No physical damage resulted from the weapon's use.
The final time Karal channeled mage energy was during the Final Storm, the one that held all the power of the original Cataclysm. Using another of Urtho's weapons and assisted by avatars, mages and spirit beings, he acted as a bridge between the physical plane and the Void, funneling the power of the Final Storm directly into the Void, thereby preventing its release into the physical world.