What are "Decks"?
When you play Clash Royale you have 8 cards in which you fight your opponent with. Those cards are called a "deck". By swapping out one card with another card you've made an entirely different deck. That being said
there are quite a lot of unique decks that can be made when you combine all the Clash Royale cards in different fashions and we like to keep track of all of those decks on Clash Royale Deck Builder and then sort them
by their usefulness, detail and other metrics.
By knowing what decks are out there and how effective they are you can get a good understanding of their effectiveness.