When you open card packs, it can happen that you receive duplicate cards. In some cases, the amount of duplicates will exceed the limit of allowed cards you can have per type (maximum 4 of the same cards for Standard rarity, 3 for Limited rarity, 2 for Special rarity, 1 for Elite rarity).
These excess cards can then be recycled and turned into resources.
How to claim resources from excess cards
To claim resources from excess cards, please go to your collection view (in the main menu, click CARDS and then COLLECTION).
There, in the collection view, you will see in the upper right corner a symbol with a hammer.
Click on this symbol with the hammer to open the recycling screen. From there, you see how many new resources you can claim and where they are coming from.
To actually claim the resources, simply click on the RECYCLE ALL button.
Your Gold cards, if you have any, will not be recycled when you click "Recycle All". Only the excess cards will be recycled.
To recycle one of your Gold cards and to turn it into resources, you need to select the gold card individually and manually recycle the Gold card.