As you know, when you win battles, you earn 5 types of resources (4 metals). These resources are ERC-20 tokens that are dropped directly into your wallet. Their main use is to craft Card boosters in order to get new cards. You can recover your resources by burning the Cards you already have & don't necessarily need, for example.
Here are the 4 resources you can win in game:
Note: You need to approve each resource in order to allow Cometh to use your resources & interact with your wallet.