Magically infused orbs called materia are the trademark of Final Fantasy VII's gameplay.
Without materia, all any character can use is his regular attack, items, and limit breaks.
Materia is categorized into five different types: magic (green), support (blue), command
(yellow), independent (purple), and summon (red). Materia must be equipped on a
character's weapon or armor, and the number of slots on the weapon or armor determines how
many materia a character can equip.
Materia is handled in the aptly named "Materia" section of the submenu.
Materia is equipped by moving the cursor to a slot on the weapon or armor and
pressing the "O" button. Select the materia you wish to use, and press "O" again.
The Arrange option will sort the materia list by type. The
Check option will show what commands that character
has available, according to what materia he is wearing. Remove
and Remove All will remove equipped materia. (Also press Triangle
when selecting a materia in a slot to remove it.) The Trash option
will discard materia. (The party can carry up to 200 materia.) The Exchange
option moves equipped materia between characters, whether active or inactive.
Note that when a character is equipped with a magic or summon materia, his stats
will be affected slightly. After every won battle, the party will receive experience and
gil, and every materia equipped will receive AP (Ability Points), which allow materia to
gain levels. When a materia gains a level, it will unlock a new ability, or make an existing
ability more powerful. If a materia gains all of its levels, it reaches "Master" status and
duplicates. The duplicate (or "born" materia) starts out with 0 AP.
Most pieces of equipment have a normal growth rate, but some have double or
triple growth rates, which means that a materia in a weapon or armor with an
accelerated growth rate will gain two or three times the AP received in a
battle. Some equipment have no growth rate, which means that materia equipped in
them will gain no AP. Another thing to consider when purchasing equipment is
how many slots are linked. Linked slots look like this: O=O
Support materia, which
must be paired with another kind of materia to have an effect, can only be used in
linked slots.