Magical Items in the Overworld cause different things to happen that are related to magical arts. These items don't do anything if the user cannot use magic.
Tomes and books are reusable items that allow or teach one how to use the spell inside. Books typically teach the user how to use one particular spell. Tomes on the other hand allow the user to use a spell right away. Tomes can also possess multiple spells, but tomes that possess more than one spell require the user to mentally select which to use. It is more practical to learn the spells from tomes that contain more than one spell rather than use them for spells. While tomes and books have a variety of spells contained within them, they will not contain summoning spells. Typically White and Black magic are found in tomes though some monster magics may also be found in books and tomes. Tomes with a single spell and books can have card effects applied. Tomes with multiple spells cannot have card effects applied. Attempting to do so will have no effect.
Magical Scrolls allow magic users to use the spell contained once and once only. Nearly all magical scrolls will disintegrate after being used. Most users obtain multiple scrolls of the same type. Since learning a spell usually requires more than one cast of it, multiple scrolls is often a necessity. Since you can learn spells from magical scrolls you will not need any additional scrolls once you have learnt the spell. Summons, monster magics and some extra spells/techniques can be found in magical scrolls. There are also technique scrolls, but these are reusable and not related to magical spells. Scrolls cannot be augumented with cards.
Cards are augments to magics. They can be used to raise different stats in addition to the base effect of a magic spell. Cards can also add effects such as providing a status rate such as poison, paralysis, etc.. The most popular application of cards is glamour, such as adding sparkles or a gentle glow around a spell. Most glamour are purely cosmetic, however some with bright/blinding effects can sometimes inflict the appropriate status ailment on opponents (or everyone looking).
It is worth noting that augmenting too many cards to a spell can cause reliability of augments to lower, they may start to periodically fail to activate or have their effects reduced. Other effects to too many cards to one spell can cause card effects to randomly override other active cards. There is also a risk of damaging a card's abilities if spells are overaugumented often.