You can enchant your equipment which has slot here. Different equipment needs different cards. You can also remove the card from the slot by consuming some diamond.
There are slots locked, and you can unlock these slots by consuming some diamond. Boss slot needs more diamond than normal slot.
You can split cards no longer needed into materials which are used to upgrade cards
You can upgrade your card by consuming materials got from splitting cards.
Collect cards to activate titles. When you activate a card, you will lose this card.