Crafting is done at a blacksmith. The blacksmith has default recipes so you don't have to find any blueprints to get the achievements. If you have enough scrap metal you can make a wide variety of low level items for 2 scrap each.
You can get your first blacksmith in Act I by completing the quest Tale of Two Blacksmiths given by Duncan in the Burrwitch Outskirts. He's very close to the Burrwitch Outskirts portal.