Magic is a confusing and advanced aspect of Higher than Hope. You don't know any magic when you start, and the only way to use magic is with either magical object such as "Chanting Gems" or Spell Scrolls to Cast magical spells.
Eventualy when you are skilled in using Scrolls, you'll be able to learn to write them into spellbooks (Gray Spellbook). However you can only write scrolls into spellbooks up to half your scroll skill's level. The advantage of spellbooks is that you are able to use more than 1 spell during battles.
Just like putting items into bags, you write scrolls into books by dragging the scroll onto the book.
At the start you are able to use every school of magic without restrictions, however as you advance you might be required to take lessons into a certain school of magic to be able to understand the scrolls.