to slot in materias will be costly depending on how much u want to slot.
it is better to ask in game.
depending on the item, u will need a crafter to help u socket the materia.
i dont suggest u do so atm unless u are using an ilvl90 crafted item cuz below those will be not worth the gil.
might want to try offgamers and see.
and when u say game card, do u mean full game digitally or just a topup card?
then come back