Crafting is a feature to replace the Trade In/Up System. It makes the process of getting a Loadout Card in the rarity of your choice easier.
Instead of Trading Up, you can Recycle your Loadout Cards for Fragments. You can Recycle all of your Lead cards, Iron cards or duplicates in a single action, to speed up the process.
Use Fragments alongside Credits to Craft a Loadout Card in your desired rarity.
If you don't have enough Credits, you can use Crafting Kits instead, purchasable in the Store.
Weapon Kits are rare items found in Arsenal Crates, allowing you to lock in on one of your Merc's three Primary Weapons when Crafting.