What is evolution? The evolution is merger two same cards into a card. The card that has been evolving will change into more powerful stat than the previous before.
|Rage of Bahamut Evolution Guide|
The best result for evolve the card is using a full enhance with 8 card. With the schema 8 > 4 > 2 > 1 (enhance in every steps). Why must be enhance before evolve? It is because you will be getting 10 % more status for your card
You need to be patient to do it, because you will be spend more rupies and cards to do it. The best way before evolving, you should farming for cards and rupies until those enough for evolving.