For those that are a bit confused:
Witchers are not magical beings, but due to the vicious, torturous regimens they undergo to become witchers, they become masters of "signs", a simplified form of magic.
The signs that most witchers (and definitely Geralt) have command over, are:
* Aard - a powerful, concussive blast of energy
* Igni - a blast of fire; witchers cannot shoot flames like flamethrower, but they can produce blasts of fire to damage enemies
* Quen - a protective barrier, similar to the Invisible Woman's shield; it protects the either against attacks, but has a short lifespan
* Yrden - a magical trap; witchers usually cast Yrden when fighting ethereal monsters, as being trapped in Yrden makes them tangible, and susceptible to the witcher's silver sword
* Axii - power of suggestion/mild mind control. Witchers can influence people
Additionally, witchers are highly trained alchemists, and can concoct potions for a variety of scenarios.
In short, the White Wolf is a motherf**king badass!