After opening the book, click "More" icon on the toolbar and then click "Cover Image".
In cover editor, click "Text" icon on the toolbar to add text, click "Image" icon to add image.
Click "+" icon on the toolbar and then click "Add Chapter" to add new chapter, click "Add Group" to add new group.
At the left panel, book structure is presented as tree view. Use mouse to right click chapter or group and contextual menu is shown.
Image icon: You can select single or multiple images from harddisk
File icon: You can select single or multiple files that CBB supports, e.g. videos, audios, pdf, etc.