Fallout Shelter

To build the weapon workshop you first need 22 dwellers, 1200 caps, and space to build a 3-wide room. The room can hold up to 6 dwellers preferably with higher-than-normal agility stats to decrease the time it takes to craft each weapon. The time it takes to craft a weapon also depends on the stats of it. Better weapons mean higher craft times. You can however use nuka-colas to speed this up. To craft a weapon you need the recipe for it and the correct amount of different junk items. You can obtain more crafting recipes through exploration of the wasteland, quests, raiders attacks, and even the occasional deathclaw.

If you need any additional explanation:

The Weapon Workshop unlocks when you have 22 Vault Dwellers and costs 1200 Caps. You can place up to 6 Dwellers in each crafting room, and more people, the less time crafting will take. You need at least one Dweller in the workshop to begin crafting.

You will have a good amount of crafting recipes, while unlocking more through exploration, raiders and lunchboxes will yield better equipment to create. You can also use Quantum to speed up the process.

Each recipe will call for Caps and a combination of Junk items that you will likely have a stockpile of at this point in the game. You can also scrap Weapons and Outfits for a chance at more scrap.