In Hearthstone, you can craft cards by selecting cards you win from card packs. Before you can craft cards, you will have to disenchant them and turn them into arcane dust. Turning your first card into arcane dust will grant you bonus arcane dust! You can access crafting mode by clicking on the top left after accessing your card collection.
Click on the blue stone at the bottom to turn the card into arcane dust and you are done. You won’t be able to get the card back, so be sure it is the card you don’t want.
Once you have enough arcane dust, you can craft a card that is highlighted in blue.
Select the card you want and craft it. The amount of arcane dust needed will vary. The rarer the card, the more arcane dust is needed.
Confirm it and you will successfully craft the card you desire!