You can create custom boards for your decks. For example, a Commander Board for your EDH deck or a Maybe Board for cards you're thinking of adding to the main deck.
To create a custom board, head to the Build page for the deck. If you have created a new deck you will be taken to the deck's Build page automatically. For an existing deck, click on the deck and then click the 'Build' link on the right of the deck's title.
Click the drop down menu to the right of the search box and select 'Add Board...'. A new board will be created and will appear below the main board, side board and any custom boards you've already created.
Your new custom board will be named Untitled Board. To rename it, click the 'Rename' button on the right of the board's title. Type in the new name and press Enter.