Magic comes in three flavors: Safe and slow, fast and fluid or reliable and rigorous. Also called ritualistic, spontaneous and spells.

Ritual

The safest way to wield magic is to carefully weave the magical energies into the desired patterns through laborious ritual. The more powerful the intended effect the more effort is required. Even a minor ritual to clean the morning drink from any poisons will take the better part of an hour. Really powerful magic can take many participants and helpers, large amounts of space, materials and days or even weeks to complete.

Spontaneous Magic

Letting the magical energy do whatever it wants and only pushing it into the general direction intended is the most dramatic, dangerous and also quickest way to create an effect. A magician still defines intent and base as well as the three effect levels (effect, target, duration), but after that, anything can happen. In game terms, the magician has to stop his roleplay at the point where he releases the spontaneous magic and let someone else describe what exactly happens.

Spellcasting

Obviously, ritual is too slow and spontaneous magic too unreliable for most cases. So magicians have aeons ago developed magical spells. A spell is a bit like a very specific ritual that has been dramatically optimized. Casting a spell takes anywhere from a few seconds to a minute at most. It reliably creates the same effect over and over. The downside is that it is more rigid than either ritual (which can produce any effect desired) or spontaneous magic (which can produce any effect at random). A spell will cause exactly the same thing to happen every time it is used. It can not be changed in the slightest.

Every magical effect has two defining characteristics that are also linked to the skills of the wizard:

Intent

Magic being an art of the will, intent is important. A magician, does not simply create a ball of fire - he creates a ball of fire in order to harm someone. That is the intent. A spell without intent is unimaginable. Intent is also binding - a Fireball (which is a harm spell) can not be used to light a campfire.
Intent is a one-word concept. Sample intents are harm, protect, control, transform.

Base

The Base of a spell is where it draws its power from, how it manifests. Again, a single word describes the base, words like fire, water, stone, death, mind, etc.
They describe how the spell works to achieve the intent.