To craft weapons in Tales of Arise, you will need to gather materials from the various enemies you encounter in the game called zugles.
Along with the materials from these enemies, you will also need to find and gather minerals that you can find in either ore deposits or chests. For example, the Astral Crystal Grain, required to make the Basic Rifle, is located in a chest in Glanymede Castle.
The other weapons in the game will require other materials that you will need to find out where they can be found. More often than not, the answer is it's a drop from a zugle you may have fought before.
If this is the case, you can always find out by viewing the enemy info page in the field guide. You can find the field guide via the main menu, so just hit the main menu button or ESC - the field guide info tab will be on the far end of your screen.
Click field guide, and you can find enemy info as one of the listed options. Under enemy info, you will also be able to see the various drops enemies have.
Check these with the materials required to make whatever sword or gun you are trying to make. Chances are one of these monsters or foes has it as a drop, and to get it will require you to farm them repeatedly.
You can farm enemies for loot very easily if you find out where they spawn. If you find a good location with a lot of the enemies you are trying to farm, you can always clear the area of them and fast travel back to reset their spawns.
Doing so is an easy way to farm not only materials but also XP, Gald, and even SP. However, sometimes you'll require materials from giant zugles to make weapons in Tales of Arise, and when this seems like the case, fighting one is the only way to make the weapon.
You can find giant zugles in various points and during a few main missions in Tales of Arise, but fighting them is tricky business as you often need to be at a high level, so you'll need to prepare by leveling up and stocking up on health items before facing them.
That said, once you have enough materials, simply take them all back to either a blacksmith or merchant at a camp to craft them into the weapon you want.
Check out some of our other Tales of Arise guides!