Crafting in Dragon Age: Inquisition is very easy and it is available for everyone - no additional abilities or specialties needed. The only thing that you need to craft an item is schematics (you can either find them in the game world or buy them from merchants), materials (you can collect, buy them, breed animals and obtain them in the mode of tactical operations, as the Inquisition advisors) and the crafting table, which is available at the smithy and in strongholds.
Crafting and upgrading is based on schematics, which is the main indicator of quality. The basic items have at best third quality class, upgrades (e.g. pauldrons, etc.) have second at best.
The second factor that affects the quality and bonuses is the material that you use. Each item to craft requires an appropriate amount of material to make so, if you need a cloth, you can use both cotton and silk or, instead of iron, you can use obsidian. You can view before you craft, what parameters the item will raise and by how much. The same materials are used for upgrading both the armors and the weapons so it is a good idea to loot everything.