Magic is mysterious and extremely diverse. It's never safe, never standardized, never fully understood. On the one hand, almost all the magical powers from other iconic RPGs may have their mechanical equivalents in the Futile Kingdoms, even with the same power levels from 0 to 9, so they're easily imported. On the other hand, you can't just pick a spell from the catalogue or buy a scroll from the local adventurers' guild.
Magicians don't have spell slots or listings of known spells. They don't have mana. Few have any inherent magic at all. What they have instead is Expertise. Magic is a field of study, and the eight traditional Schools of Magic are familiar looking subfields. The magicians' job is to interpret and manipulate the magical phenomena that are already in the world. To do so, they must travel far and wide to find mentors and hidden knowledge, carefully study books and artifacts, or conduct their own experimental research. All of this is dangerous and uncertain, not only because of social barriers and stigma, but also because of the unpredictable nature of magic itself.
How does this work mechanically? Magic spells are always bound to some physical entity, so they can be tracked as inventory items or places in the world. It could be a magical ring, a bag of beans, a laser shooting sword, a genie in a bottle, a prepared ritual space, etc. -- all called spells here for brevity. They can be used by anyone who finds them. The hard part is figuring out how to use them properly. The GM knows exactly how each spell works and what risks are involved, but the players don't. They must rely on Expertise, folklore, logic, intuition, experimentation, and luck. They can cast their spells repeatedly, but a terrible accident might always happen, or the power source might simply run dry. With time, they come to understand their spells better, but there could always be something they don't know. What's worse, every spell is a little different, or works differently for different casters. This makes up a great part of the variety and sense of discovery of a campaign.
New characters are given a starter spell or two to get going. These are largely "stock items" for convenience's sake, although they might come with a little twist. Players who want more must find it in the world, by looting or other ways of exploration. With enough time on their hands, characters can look for their own magical solutions to specific problems. All they need to do is collaborate with the GM, who may respond with an appropriate set of challenges (and hidden "bugs").