Folders are a way to manage your library, making it easier to find the decks you're looking for.
To make a new folder, go to the Library tab and click the "New Folder" button in the top left corner.
You will be asked to name your new folder, after which it will appear in the top left corner. To add decks to a folder, simply click and drag the deck to the folder. The deck will now appear when you click on that folder.
Note: You can put decks into more than one folder, and decks in a folder will still appear when you click on the "All" folder.
To remove a deck from a folder, select the folder, click the blue Action button, and select Remove. This will remove the deck from the current folder.
Caution: Make sure to click "Remove" not "Delete". Clicking Delete will remove the deck from your Library and you will need to repurchase the deck.
To remove a folder, select the folder to open it, and then click Remove. You can also Assign or Rename a folder when in the folder view.
Our video on The Library shows you how to use Folders: