To properly load a book, hold the book closed with the cover facing up toward you, fit the top end of the bookbinding into the top of the unit, then lower the bottom end of the book binding into the bottom of the unit.
Make sure the back cover of the book is lying flat against the right side of the base unit.
If the book is open to any inside page, make sure the front cover is lying flat against the left side of the base unit.
Make sure all other pages are lying flat.
Make sure the book is not upside down.
You may play with only one book at a time when inside the unit.
The alphabet on the base unit does not work if a book is loaded into the unit (even though you can see half of the alphabet when using the front cover or back cover of a book.)