The Dwarf Merchant is a point of interest you will encounter early on. Tap on the Merchant map icon and you can access his shop.
He has a rotating stock of items on display: Forge Materials, Shards, Upgrade Cards, Potions of Knowledge, and Gold. Some can be purchased with Gold, others with Diamonds. He also always has one of his six offers on sale!
The Merchant restocks his display twice a day, but you can also refresh his offers for 50 Diamonds at any time.
While you progress and increase your Warlord Level, the Merchant will also have better items on display for you. He will always be a helpful partner for you and your army.