Spells
A spell is a discrete magical effect that manipulates the very fabric of reality. A spell's text describes the game mechanics for it. Spellcasting details the requirements to use magic.
Every spell has some Spell Attributes that determine important mechanics about it.
See Spell Indices for the list of spells recorded in the Imperial Library.
Crafting
PCs can learn how to do Basic Alchemy with an Alchemist Kit.
High level PCs can look into Crafting Magic Items using the spells they know.