At the moment spells are fully passive buffs - there's no casting UI. Each spell belongs to one of six schools (crit, mend, travel, sight, undead, rarity), and your best spell in each school randomly "procs" on its own during play, spending 1 MP to do that school's one job: land better hits, heal you, speed travel, and so on. You learn new spells at rank-ups and events, and higher spell degrees plus WIS just make those procs fire more often.
I am planing to develop that system in future updates.