Below is a walkthrough for the Forge a Weapon task in Rune Factory 5.
Client: Martin
Objective: Craft a weapon using your forge
Reward(s): Bronze x1, Iron x3
This task will show up on the Task Board after completing the Buy a Forge task. After accepting the task, Martin will task you with using your forge to craft a weapon. If you have any recipes that you also have materials for then feel free to craft those. The easiest thing to make is the Broadsword (short sword recipe) or the Claymore (long sword recipe) which both require a single mineral such as scrap metal or iron to craft. You can usually find them by smashing rocks with your hammer. Once you craft the weapon, return to the Task Board to complete the task.