Go to the Collection menu. You’ll see all your decks there. On the top right press on Create Deck.

First, you will be prompted to select a Warlord. This will determine which faction cards you can use, and what Talent you can expect from your Warlord. Choose your preferred one and drag it to the left side of the screen where your deck cards will be stacked.

Upon confirming your Warlord selection you will have a list of 30 cards to fill to the left of the screen. To the right you will have a list of all your owned cards available for that Warlord. Drag cards into your deck until you have 30. Press on any card to see more information about it.

On the top-left of the screen you will find the  Filters button. When pressed, it will display the filters panel over the decklist. You can filter cards by Energy cost, Rarity, card type (Warlord, Troop, Stratagem) and more.