Spells are not picked from a list. You build them, and the same three parts recombine into everything you will ever cast: a sigil that sets the element, a form that decides how it leaves your hands, and modifiers that change what happens when it lands.
Sigils
A sigil is the elemental root of a spell: fire, water, wind, light and the healing arts, the five disciplines the Great Witches taught when magic was still public. Every recipe takes exactly one. Swap the sigil and keep everything else and you get a different spell with the same shape.
Forms
The form is delivery: a bolt, a cone, a ward, a lingering field, a shape drawn on the ground that waits for something to walk into it. Forms carry most of a spell's cast time, so a heavy form is what makes a spell obvious in public.
Modifiers
Modifiers are the expensive part. Each slot shows its real cost before you commit it, so nothing is a surprise once you cast. Two modifiers pulling in opposite directions will fail the recipe rather than average out.
Quick casting and hidden casting
Because magic is still a secret, every spell can be cast two ways. Quick casting is fast and risks being noticed by anyone nearby. Hidden casting takes about twice as long and mostly is not. In a fight that is a real decision: the fast version wins the exchange, the slow version keeps your name off a report.
Build two versions of every spell you rely on: one light enough to hide, one heavy enough to end a fight.