You have learned how to cast rituals. Rituals are spells which are written in a ritual book, which you must have in hand while casting one of them.
When you choose this feat, you acquire a ritual book holding one spell from a theme you know with a mana cost of 1 and the ritual tag.
If you come across a spell in written form, such as a magical spell scroll or a mage’s spellbook, you might be able to add it to your ritual book. The spell’s mana cost can be no higher than your mana limit or psi limit, and it must have the ritual tag. The process of copying the spell into your ritual book takes 2 hours per level of the spell, and costs 75 sp per mana. The cost represents materials you expend as you experiment with the spell to master it, as well as the fine inks you need to record it.