The instructions for performing incantations are generally found in various obscure tomes. Such books are filled with “magic spells,” and most of them are utterly bogus. But hidden among the dross is the real stuff, and discerning whether an incantation found in a book will actually work is a matter for experts in arcane lore.
Finding a set of instructions for a particular incantation requires a successful Research check with a DC equal to the Knowledge (arcane lore) DC for the incantation –10. Just learning of the existence of a particular incantation is an easier Research check, with a DC equal to the Knowledge (arcane lore) DC –15.