I wasn't exactly sure which thread t post this in so i decided this one. I have a spell book in my inventory and was wondering i could add spell to it so i can learn more. As in my campaign i learned a new spell but don't know how to add it to the spell book.

Spells are not added to the book but to your character. Presumably you are  wizard as spellbooks are a wizard thing. On your sheet click spells, then manage spells and then Add Spells. You can then add the spell you learned.

How does one do this if they are not a wizard? One of my characters was "gifted" a spell by his deity, but I can't figure out how to add it to his list without having to remove another spell.

Hes a warlock if that helps?

You will need to homebrew a magic item that grants it, bearing in mind it will not use spell slots - you can limit usage through spell charges on the item, or create a homebrew version of his subclass that grants the spell.

Quote from Lazersharkzzz >>

I wasn't exactly sure which thread t post this in so i decided this one. I have a spell book in my inventory and was wondering i could add spell to it so i can learn more. As in my campaign i learned a new spell but don't know how to add it to the spell book.