Crafting is a means of obtaining cards without buying packs. It is currently the only way you can collect cards without relying on random chance from either packs or rewards from various game modes. Cards are crafted with varying amounts of Arcane Dust () depending on their rarity and quality.

Cards fall under various categories that effect whether they can be crafted or not. Those rewarded from Adventures for example must be earned by playing their respective wing. Golden versions of those cards can be crafted at the appropriate price however. Others such as Soulbound cards earned by leveling up your heroes can't be crafted in either form. Then there are promotional cards like Elite Tauren Chieftain and Gelbin Mekkatorque which can only be obtained through crafting.

Arcane Dust

Arcane Dust is a resource obtained by either disenchanting cards or from Arena rewards. You spend dust to acquire cards and disenchant cards to acquire dust.

Except in very specific circumstances, this is how rarity effects dust:
 
 
Rarity Crafting Disenchanting
Common Normal - 40
Golden - 400
Normal - 5
Golden - 50
Rare Normal - 100
Golden - 800
Normal - 20
Golden - 100
Epic Normal - 400
Golden - 1600
Normal - 100
Golden - 400
Legendary Normal - 1600
Golden - 3200
Normal - 400
Golden - 1600

Disenchanting

Disenchanting is a means of deleting cards you have extra of or no longer desire. Hearthstone will automatically detect when you have more than two copies of a card (or one of a Legendary) and give you a single option to disenchant all extra cards. All players do this as there's currently no reason to hold onto more cards than are playable in a single deck.

One of the largest decisions you'll make when playing Hearthstone is whether or not you want to collect golden versions of cards. They're pretty hard to come across, especially those of the higher rarity, and are worth significantly more than their regular counterparts. If all you want is a full collection of every card in the game, it might make sense to just disenchant each golden card you collect. Others prefer to keep higher quality versions of those that they actually use, while the most hardcore hold onto them all as that extremely unlikely, complete golden collection looms off in the distance.

As a general rule, disenchanting a golden version of a card gives you enough arcane dust to craft a regular version of equal rarity. So a golden legendary nets you any regular legendary. The same goes for epics, rares, and commons. Normal versions are only worth a fourth or less of their full crafting cost. For this reason, the fastest way to grow your collection is to disenchant all golden cards in favor of cards you don't have.
 

Crafting

Crafting is how you spend arcane dust and grow your collection. Though many players save up dust in an effort to craft Legendaries as it's very difficult to actually unpack every one in the game, the most competitive players will tell you that it's actually the Epics that get most people in trouble. There are currently 93 in the game and you'll need two copies of many of them. Some of these completely determine whether or not you can run a specific archetype. There can be no Freeze Mage without Ice Block, no Midrange Druid without Force of Nature or Ancient of Lore, or Control Warriors without Shield Slam or Brawl. There are many crucial Epics that decks rely heavily on, but the majority of players tunnel onto growing their Legendary collection.

Keep this in mind: With the 1600 dust to make one Legendary you can craft four Epics, 16 Rares, or 40 Commons. New players really should focus on crafting those important cards that decks frequently depend on. There is no deck that is completely ruined by the lack of Sylvanas Windrunner. Yes, there are those that really do need cards like Archmage Antonidas or Malygos, but most decks in Hearthstone can be run without these.

Special Cases

Since Blizzard launched Hearthstone, it has set the precedence that if any card is changed (for better or worse), you will temporarily be able to disenchant it for its full cost. For this reason, Leeroy Jenkins was temporarily worth 1600 dust when disenchanting a normal version of it. That's a 400% increase in value.

Keep in mind that this is only for cards that you can craft. When Undertaker was changed, there were no repercussions as it's only obtainable through Naxxramas. Others like Warsong Commander are basic cards and are obtained by leveling up and therefore will not net you any extra dust when nerfed.
 

No Trading

You may ask why you can't simply trade cards with friends. Blizzard spoke about this back in the beta days of Hearthstone:

 

Originally posted by Blizzard (View Original)Collapse

Why can’t I just trade my cards with my friends to get the cards I want?

Many card games out there are considered “Trading Card Games,” or TCGs. While there are perks to being able to trade your cards, there are negatives to card games that support trading, even in a digital world. What do you as a player want out of trading cards? Generally, the answer is “To get the cards I want and trade away the cards I don’t!”

What happens when the cards you have are the “wrong” cards—cards other players simply don’t want? What about when everyone wants the same cards?

When a player opens a pack of cards in a typical TCG, they’ll generally find a fixed number of cards of various rarities. Cards of the most numerous rarity in any given pack, or “common” cards, end up having little to no value. Everyone has them and no one wants them.

What about the rare cards? These “more valuable” cards can vary wildly from “MUST HAVE!” to “meh” and anywhere in between. In a trading system, the unimpressive rares end up being only slightly more valuable than common cards, even if they aren’t nearly as common. It’s very common for a dozen or so rare cards from any given set to contain most of the value and the rest are worth very little. People demand those high-end cards, and their value skyrockets. Can’t afford to buy all of the good rares? You better hope you’re lucky when you open your next pack.

So in a trading-based card game, you may finally manage to get a card that is “worth” something . . . but then you want to keep that card and not trade it away. So your only option is to purchase more packs until you get something worth trading, even if you may not actually want to part with it. That’s not particularly fun. On top of that, you may even feel like you can’t play the game competitively without that specific card! It’s very frustrating, and new players are reluctant to become invested in a card game if they can’t manage to get those cards—in trade or for cash.

Crafting allows you to get the cards you’re actually looking for without having to wait for random luck to shine your way, with no need to look for people that have a particular card you want to round out your deck.

Hearthstone allows you to disenchant your Expert cards into Arcane Dust, and you then use the Arcane Dust to create the cards you want, instantly! It’s fast, it’s easy, and you don’t have to reference how valuable your card is on a secondary market each time to want to make a choice to trade it off or not.