You click the 3 line menu button in the top right, and then click on My Settings to access some more advanced settings.
Replace or Add Candids: When you drop a new image on a page and it is above an existing image, some people prefer to add as a new image and some people want it to replace the existing image. You can set the default behavior to one or the other, or to explicitly ask every time.
Grid Lines: If you want to see grid lines to help you line everything up exactly, turn this option on. You can change how many inches between lines and what color the lines are.
Alignment lines: By default when you move image or text nodes around, they will snap to each other to make lining things up easier. If you prefer, you can turn these off so there are no automatic alignments.
Show Candid Stats: If this is checked, how many times an image is used in a book is always shown instead of requiring you to hover over the image first.
Advanced Editor: This option turns on some advanced options such as showing the position and size of each node while you are moving or resizing it.
Ctrl + Z: Undo last action
Ctrl + Y: Redo last undo
Ctrl + Shift + Z: Redo last undo
Arrow keys: Move image or text box
Shift + Arrow keys: Move image or text boxes in smaller increments
Ctrl + C: Copy selected node(s) to past to another page
Ctrl + V: Paste previously copied node(s) to the currently selected page
Ctrl + A: Select all editable nodes on the currently selected page
Ctrl + +: Zoom in
Ctrl + -: Zoom out
Holding the Ctrl key while doing certain actions allows you to do different actions in certain cases:
Holding ctrl while clicking and dragging an image allows you to edit the crop on the image
Holding ctrl while you resize an image allows you to resize the image without holding the aspect ratio. The crop for the image will automatically be changed to keep the image from getting squished.
Holding ctrl while you use the mouse wheel while selecting an image allows you to zoom in/out on the crop.
Holding ctrl while you drop an image onto a page automatically puts it behind the cells on the page
If you have an image behind a subject cell which you can't select, hold ctrl and it will select the image behind the cell.
Holding ctrl while you use the mouse wheel while not selecting anything changes the zoom level for the entire page
Pressing "Move image back" button on image toolbar while over a subject cell changes the image to be behind the subject cells
Pressing "Move image forward" button on image toolbar while over a subject cell changes the image to be overlapped in front of the subject cells