How to use spices:

Open the synthesis house → click "Card Production" → select the recipe of the card you want to make → if the recipe requires all the materials, continue → there is spice in the lower left corner Selection bar → You can add a spice if you have 5 of it (if there are less than 5 unbound ones, but there are 5 in total with the bound ones, you can mix the spices, and the card created is bound) → Click "Create" → automatically consume 398 gold coins → successfully produced