Decks store the context of what you are trying to do. This could be a list of to do items, completed items or items classed by their requirements such as art, gameplay, players, enemies, graphics, levels, etc.
Click on the Add Deck section to add a new Deck
Name the deck
Note that you can also drag the decks around to reorder them.
Decks by themselves are not great. They are used to keep similar ideas or tasks groups together. These tasks are called cards in codecks.