The book has 6 pages. Each page has a different function; WIRE, NOT, OR, AND, XOR and LATCH. Sensors in the book detect which page you are on so that the buttons can have different functions depending on the active page.
For example, when you are open to the NOT page the LED is on as long as the button is NOT being pressed. And on the AND page, the LED lights up when both buttons are being pressed. Each page lights the LED with a different color.
The book contains a small replaceable battery. From the back cover, you can remove the battery flap, and with a screwdriver remove the set screw to get access to the battery.