The wandering dwarf Haldor will be one of the few characters in the game, always happy to see you. To buy something from him, you need gold coins. However, several things can be sold to him.
Among all the resources that you can find in the world, there are those for sale only. Simultaneously, you cannot accidentally sell useful items; the merchant will not accept them. It turns out a simple pattern; when you cannot create something for sale, you have to find it in the game world.
The merchant buys amber, amber pearls, and rubies. They can be found in several different places:
Chests in abandoned buildings (most often found in meadows);
Burial chambers in the Black Forest (most often found in the Black Woods);
Troll Caves in the Black Forest (rock formations with a large entrance, indicated by piles of bones);
Sunken crypts in the swamp (dark and gloomy dungeons that can be opened with a swamp key).
Troll Caverns are excellent sources of loot. After fighting the trolls, you can immediately get some gold.
Amber, amber pearls, and rubies can be used to create jewelry. However, this will be much less useful than any of the items purchased from the merchant's assortment.
Amber - 5 coins;
Amber Pearl - 10 coins;
Ruby - 20 coins.
The game even has its internal meme on the topic of quick money. One Viking dances on a platform like a pole in the same name's video while another throws coins at him. The dancing Viking strips and gets even more gold. Of course, this is a joke, and the like is ineffective.
There are no other ways to earn and spend money in the game. You will not be able to find the merchant right away, so you will have already collected a certain amount by the time you meet. Even if you bought all of the items from Haldor, keep in mind that the game is still in beta. New opportunities for earning and spending may appear very soon.