To add a new book to your e-Library click on the appropriate icon in the toolbar or select Books -> Add New Book... This will open an empty Book Card where you can enter any book data (genres, authors, format, language, etc).
If you adding an electronic book, you'll want to attach the book file in the File tab. Besides, you can retrieve book ISBN using the tool in the Book Card toolbar.
Having entered the book title you can update the book data from the Web. You can also download the book cover from Google Images in the Cover tab.
Press the OK button to save the Book Card.