If you want to import decks from a text file or .dek files on your hard drive, check out this article. If you want to start from scratch, read on.
Starting a New Deck
You can start a new deck by clicking the “New Deck” icon in the lower left corner, or in the deck area if no deck is open. You can also double-click on a card or right-click on a card when no deck is open to start a new deck containing that card.
If you want to edit a deck you already have, click on a format filter in the lower left to view your decks, and click on a deck name (or a deck icon in the lower right area).
The Collection scene is divided into four parts: Filters in the upper left, Matches in the upper right, Decks & Binders in the lower left, and the deck or binder itself in the lower right.
Use the Filters section and the drop-down menus across the top to adjust what cards appear in the “Matches” section, and how they will be displayed.
The default view is to show your collection in piles, but you can switch to a list view using the “Display” drop down.
To view cards not in your collection, adjust the slider in the “Quantity” drop-down to include 0.
To see each version of a card in a separate pile, check the “Show versions separately” box in the “Versions” drop-down menu.
Building and Editing a Deck
To add cards to the open deck, you can double-click on a card in the Matches section, or right click on a card and choose one of the “Add…” options in the subsequent menu.
Your deck will be auto-saved as you change it; there is nothing to click to save your deck. If you are just tinkering and don’t want to overwrite your deck contents, right-click on a deck and choose “Open a new copy of this deck” in the menu.
If there are any problems with your deck given its format, you will see a caution icon next to the deck name. Right-click on the icon to view a list of the problems with your deck.
You can sort and view your deck in different ways; explore the options by right-clicking in the deck area. You can also adjust the dividers between the four sections of the Collection tab, allowing you to customize your view.
If your deck is constructed legally and all the cards in it are in your collection, there will be no caution symbol and you are ready to play. Head to the Play Lobby and find a challenger!