On this page of the guide to Horizon 2 Forbidden West you'll find information on how to earn Metal Shards which serve as the game's main currency. You'll also find tips on what to prioritize spending money on.
Metal Shards - in-game currency
Horizon Forbidden West doesn't feature traditional money - gold, dollars or credits. The basic currency (and crafting ingredient) are Metal Shards. You can check how many you have in the upper-right corner of the menu windows.
Metal Shards are the main currency, but some major purchases require you to pay with other resources as well. In an example pictured above you need both Metal Shards and some rare machine components.
Smaller purchases, such as consumable items or singular crafting parts, usually require only Shards.
How to earn money?
The best way of earning Metal Shards is looting. Search all the containers you see, all scrap piles, destroyed machines and killed enemies.
When it comes to loot, usually the more difficult it is to reach, the more valuable it should be. This means that destroying elite high-level machines and looting hard-to-reach containers should reward you with plenty of Shards.
You can also sell useless or unwanted items from your inventory. The items in the former category are primarily valuables which only exist to be sold. You must be careful with other items - rare components can be useful for crafting later on, while various outfits and weapons can come in handy during specific quests and battles.
Completing quests usually doesn't reward you with funds - instead you receive XP, skill points or unique items.
What to spend Metal Shards on?
You can spend Metal Shards on many different things, which means it's easy to run out of them. You should prioritize some purchases and activities while making sure you always have some Shards to spare.
The most obvious use of Shards is trading with merchants. You should especially focus on weapons and outfits, but make sure everything you buy will actually be useful, having better stats or quality than your already owned gear or being entirely new (such as the Ropecaster or the Warrior Outfit).
It's usually not worth it to spend Metal Shards on consumable items. Many of them can be looted in the game world and crafted.
Another potential use of Metal Shards is upgrading your gear - weapons and outfits. You should plan your expenses wisely though. There is no point in upgrading items you're not going to use often, like weapons and outfits with low stats or those not fitting your playstyle.
Prioritize upgrading the gear you use often to increase its stats and give it new features.
The last category is crafting ammo. You must be aware that Metal Shards can be used as ingredients for making various arrows, bombs and other projectiles.
The better and more unique the ammo type is, the more Metal Shards you may need to craft it. Keep this in mind and don't waste rare ammo on weaker enemies if regular ammo would also do the trick. You can also loot ammo along with other items.