Inventory

In your inventory you can check all the cards, crystals, blueprints and trophies you have. By selecting between Cards, Craft or Trophy you can check all what you have. 

In cards you will find all the cards that you have. To equip a card you just need to go to Inventory - Cards. Then drag the card you want to the bar under your avatar. If you have all the slots complete or you want to change a card just drag the new one over a used slot and card will change. You can always clean that bar by selecting Clean Action Bar.

You can also use the filter the game gives you to choose which cards you can check. For example you can sort them out by timers.