The deck editor is designed to be interactive and easy to use. There are however a lot of features in the deck editor (with more on the way), so here is some helpful documentation about each feature.
Creating a new deck
You can create a new deck in the start screen and using the menu action
File > New Deck.
When you create a new deck, it has no name/file.
You can name it when you save the deck.
Opening a deck
You can open a deck using the start screen action, or the menu action
File > Open Deck, or with the keyboard shortcut (Ctrl+O).
Searching for cards
Note: The filter is currently considered experimental. Report any problems here
You can use the bar on the right hand side to search and add for cards. The filter allows you to search via things like card type, attack, attribute and more.
The pagination at the bottom can be used to toggle between pages.
Adding/Removing cards from the deck
You can move cards about by dragging them. Additionally, you can right-click to add the from search, or remove them from the deck.