Models that can cast spells are known collectively as Wizards, although specific armies might use other terms.
Before we get into discussing the Magic phase proper, it's worth taking a little time to introduce the idea of Wizards and their spells. Only beings that possess awesome mental might can even hope to bend the powers of magic to their will. Lesser persons would be consumed in an instant, their souls torn apart by unfettered energies or devoured by cackling Daemons. Even the most accomplished of sorcerers walk a narrow path at the edge of sanity, between ultimate power and total annihilation. In Warhammer, we commonly refer to a model able to cast spells as a Wizard. Some races use different terms, such as sorcerer, shaman or seer, but all of these and others are considered to be types of Wizard.