As you walk around the world in Nexomon: Extinction, you will come across stones filled with multi-colored gems. You can break these stones to collect the gems as long as you have a pickaxe. Fortunately, you can grab a pickax pretty early in the game, and you should definitely get it as quickly as possible from the NPC near the orphanage. This will allow you to farm shards as soon as you start playing the game, and you'll need a lot of them.
You can use Shards to exchange them at the General Store for gold, as a way to get items from some wandering traders, and you can use them to synthesize hearts. Cores are very useful items that you can equip on your Nexomon to improve their base stats.
Hearts are certainly the most important use of shards, so be sure to sell some that you don't need to upgrade your Nexomon. Truth be told, gold isn't hard to find in the game, so there's no reason not to save your shards for synthesis and trade.
How to make synthetic hearts
You can synthesize the cores once you get to Parum. To access the building you need to be in the Synthesis Cores, go directly to the left of the Parum Warp Stone until you exit the screen. Cross the bridge then go north. You will come to a large fountain with an ornate building directly behind it. This is where you need to go.
At the back of the building, you can find Bonnie and the Synthesis Machine. Here you can choose from a row of hearts, at different ranks, and use your shards to create them. Each core requires a different amount of shards, of varying types, for you to synthesize.
