Magic in the world at Dawn can be quite a bit more powerful than in other settings. But it is also more complicated, this page will explain the system.

Learning and Casting Spells: When a character takes the Arcane Background (Spellcasting) Edge, he selects a Thread with which he has an affinity. This is his Primary Affinity, and usually determines a great deal about the mage’s outlook on life.
When a casting a spell
Step 1 Determine Effect, first the caster must determine what he wants his spell to do, and how he wants to do it according to his Affinity (or Affinities).
Step 2 Determine the PP cost by checking your desired effect against This Table
Step 3 Make a spellcasting roll with all appropriate bonuses and penalties. You take a penalty on this roll equal to the PP cost of the spell. These penalties may be negated, as listed under Evocation and Thaumaturgy.
Step 4 If you succeed, apply the effect. If you succeed with a raise, the spell costs one less PP to cast. Every raise reduces the cost of the spell to a minimum of 1 PP
Step 5 If you fail, determine whether you will take the unleashed magic energies into your self as Backlash and cast the spell as planned, or unleash them on everyone and everything around you as Fallout, letting the energy run loose.

Evocation is the type of spellcasting represented in the core rulebook. It is the type of spellcasting to use when you need to be invisible, shoot lightning, or blind your foes right now. It is quick, dirty spellwork which is often required in combat. It takes an action to cast an Evocation spell. There are two ways to negate spellcasting penalties with Evocation. The first is by designating Rote Spells. A Rote Spell is a set effect which the caster has practiced frequently, and thus can use much more efficiently and reliably. A Rote Spell’s PP cost is reduced by 1/2, rounded down! The caster may have a number of Rote Spells equal to 1/4 his smarts die, rounded down. These spells must always be cast the exact same way every time, including a use or lack of a focus items.
The second way to negate penalties is the use of a Focus Item. These items, traditionally (but not always) wands or staffs, are each attuned to a certain Thread, and grant bonuses to cast spells tied to that thread. You may have any number of Focus Items, but making a focus item is a taxing process. Creating one takes 3 days of uninterrupted work, costs $200, and uses up all the casters PP during those three days. A focus item grants a +2 bonus on Spellcasting rolls made to cast all spells tied to its attuned thread. A caster may only benefit from a single Focus Item on a single spell.

Thaumaturgy is the type of spellcasting used when you need to cast a powerful spell that would normally be too difficult for you to cast, or want to be sure that your spell won’t blow up in your face. Thaumaturgic spellcasting is based a second Arcane skill. A character who takes the Arcane Background: Spellcasting Edge gains both the Arcane: Evocation and the Arcane: Thaumaturgy skills. When a spell is cast using the Thaumaturgy skill, it is called a ritual.
Determine how many power points the ritual will cost. The caster can mitigate this cost in several ways. If cast on a Ley Line (not near- on), 1/4 of the power points can drawn from the line. If cast on a Nexus Point, 1/2 of the power points for the ritual will be supplied. The caster can also draw power points from others. Willing participants (who must be present for the whole ritual) can contribute as many points as they desire (characters without an Arcane background edge are assumed to have a number of points equal to 1/2 their spirit die). Unwilling participants can also be used. To draw power from these sources, blood must be drawn from the helpless individual during the course of the ritual. This automatically deals a wound (incapacitating extras). Any amount of points up to the individual’s maximum can be utilized. Finally, if a unwilling participant is instead killed during the ritual, their life force can be used to fuel the ritual, providing triple their maximum power point amount.
The next step is to determine the modifiers to the casting skill role. A penalty is applied equal to the total, original PP cost of the power. As with the power point cost, there are ways to mitigate this penalty.
First, materials can be used to help the caster. By expending $50 in material components (ritual candles, rare herbs, foci items), the caster can negate a -1 penalty. The caster may negate up to half the ritual’s penalty in this way.
Second, the caster can take extra time to ensure he is doing everything perfectly. By doubling the casting time, he negates a -1 penalty. For every modifier above that (x3, x4, x5 and so on) another -1 penalty can be negated. All of the ritual’s penalty may be negated in this way.
Third, the caster may apply conditions to the ritual. He is encouraged to work with the GM to come up with neat, flavorful restrictions for the ritual. These restrictions can negate anywhere from a -1 penalty for minor considerations (needs to be cast during the nighttime) up to -10 or higher for particularly difficult restrictions (can only be cast at midnight on the Winter Solstice, requires rare ritual focus which must be found, cannot be bought, etc etc).

Backlash and Fallout: Though magic has much more potential in Entropy than other settings, it is also more dangerous. Magic is the chaotic raw untamed energy that exists between realities. Unlike psychic abilities, gamma-tech, alpha powers, or faith abilities, magic is not tame, reliable, or controllable. Anytime a caster fails his Spellcasting roll, he incurs Backlash, or unleashes Fallout!
Backlash occurs when the caster contains the unleashed energy within his own body. If he failed the check by 1, he is shaken. He takes 1d4 points of damage for every additional number by which he failed his roll, and this damage is unaffected by armor. However, the benefit of taking backlash is that the spell works as intended, even if the caster falls uncoscious or dies immediately thereafter! Failed Thaumaturgy spells may not be taken as Backlash, they always are released as Fallout.
Fallout occurs when the caster looses the untamed magic on the world around him. His spell automatically fails, and the magic is let loose upon the world. A good rule of thumb for this is to expect everyone (excluding the caster) and everything in a large burst centered on the caster to take 1d6 points of damage per 1 PP cost of the failed spell. HOWEVER, the GM is encouraged to get creative with this. Perhaps the spell works, but targets the wrong people, or maybe the spell works in the exact opposite way intended!
If The caster rolls a 1 on both the Spellcasting and the Wild Die, horrible things happen. If the spell is taken as backlash, the damage increases to 1d8 per number! If the spell is unleashed as Fallout, the GM can and should be extremely creative in coming up with awful things which happen to the caster (and the party)! Unlike other rolls, however, Bennies may be spent to re-roll critical failures on Spellcasting checks.

Ley Lines and Rifts A character with the Arcane Background: Spellcasting edge regains power points twice as fast when within 100 meters of a ley line. A character within 100 meters of a nexus point instead regains power points four times faster than normal. These benefits stack with the rapid recharge and improved rapid recharge edges, thus a character with those edges standing on a Nexus point would recover a powerpoint every 4 minutes! This advantage explains why kingdoms which rely on magic, such as the Empire Arcana, will establish cities on Nexus Points if possible, despite the risk of a Rift opening.