From Gamesverse Wiki
Spells are designed and written, in a manner similar to a computer program (though the analogy is not perfect, and there are ways in which it doesn't fit). The style is, for lack of a better word, the programming language, and some will be better at certain things than others - Mid is good at shooty spells and defence, whereas Ancient Belkan is better at close up smash-or-hack-you-apart, etc.
Writing or designing a spell basically means sitting down, working out everything you want the spell to do, and then putting together the components to do it. Generally, this is a slow process of several weeks as you go over the formula with a fine tooth-comb to optimise it and make it as efficient as possible, remove any potential glitches, ensure it's safe to cast, etc. You're also required, if it's a combat spell, to put in TSAB-mandated safeguards if you want it to be legal.
For instance, a shooting spell like Divine Shooter is a fairly simple one. It creates two parcels of mana, imbues them with a momentum vector along which they travel, which is set before they're fired. There's a tricky little bit of coding that allows you to paint a target which they will then home in on, and when they hit they deliver a force to the target like a sledgehammer blow - this last bit is where the safeguards are, they're part of the program that means that if you want to raise the force variable to levels that would be lethal, you have to override the safeguards in order to do so. Your Device will look at the target and allow you higher "safe" levels if they're another mage, and thus wearing a Barrier Jacket, than if they're an unarmoured civilian.
These safeguards, since they're selective and dependent on the target, are reasonably complex. They're required for all TSAB-legal spells, and using combat spells that have been stripped of their safeguards can earn you jail time. Some spells are easier to put safeguards onto than others, of course - Divine Buster is used against a single armoured target, and can be micro-handled by the Device for that, but it's too strong to be used on civilians and so it won't let you do so without overriding it. Starlight Breaker... they're there, but there's no real way to make "I AM BECOME NUCLEAR GIRL!" completely safe, and the safeguards there are in large part to remind you not to fire it near where there might be undefended civilians.
Importantly, Gamesverse magic is not like Harry Potter magic, or equivalents to it. You do not get outbursts of "accidental magic" where kids turn teachers' hair blue or levitate the kitchen table, anymore than you get outbursts of "accidental differential equations" where kids spontaneously solve the Bernoulli equations for a viscid rotational fluid in a stationary reference frame. Magic is a force that needs to be consciously controlled by someone who knows what they are doing and understands the physical laws and forces they are manipulating - generally using spells - and which is relatively difficult to draw on in the first place without a Device of some sort helping, especially when you're doing it for the first time. Nanoha cheated, she had Raising Heart to do essentially all of the work, that first time. Other mages wouldn't have been so lucky.