I call this spell craft, or spell work, because I believe that once you have learned the basics of spell casting you can and should create your own spells. Feel free to use the many wonderful spell books as bases, yes, but always tailor a spell to your own particular wants and needs. They will be far more powerful for you.
This is because the purpose of a spell is to focus your own mind, your own power. Certain words are power words to you, or perhaps certain stones or crystals, or a wand, candle, tarot card, or other ritual item. Because that particular thing engages your mind, your emotions, they will be the most effective when you are casting a spell.
(As this will be a book someday - someday this will be the introduction to this section. Doesn't work as well on Wattpad, of course, but I would like to keep it all together and in order here. In case my electronics decide it might be tasty...)