The Hearthstone website has a preview to explain how the crafting system works.
You can buy Expert cards with gold or realm-money. There are 4 types of Expert Cards: Common, Rare, Epic and Legendary. Each of these can be disenchanted into Arcane Dust.
With this Crafting System you go find the card you want for your collection and spend Arcane Dust to acquire it.
Players can also enhance the appearance of their cards with Arcane Dust to make Golden versions. The cards get beautiful frames, and even special animations which set them apart from normal cards. At this point these are for aesthetic and bragging purposes. There is no enhancement or benefit to them.
The new Hearthstone Crafting page offers some examples of the cost of each type of card. Numbers aren’t final.