You'll find the Play button beneath your book on a bookshelf, or in the top right of the toolbar when in editing mode.
When you're in Read mode, you'll see that the background is darker and the pages of the book turn nicely. All video and audio will play and links will start working too.
You can turn the pages by clicking the left or right arrows, dragging the pages with your mouse, or swiping (if you're using a touch screen). You can also use a keyboard and use the left and right arrows to turn the pages.
In the toolbar are a few options for reading:
Go full screen. The first icon in the toolbar will make the book display full screen. Click it again to return to the normal view.
Share your book. The share icon will show different options depending on whether you are reading a published version of a book, or you are in Read mode in your own book.
Settings. The cog icon has the following settings (most of which apply to the 'Read to me' function:
Display - toggle between side by side pages or single page view.
Voice - Choose the language you would like read in. Some languages have more than one reading voice option, but it depends on which browser you're using.
Highlight words - Toggle on/off.
Turn pages automatically - Toggle on/off. The pages will turn automatically by default and the book will keep reading.
Play multimedia - Toggle on/off whether or not to play and audio hotspots or embedded video whilst reading.
Slow speech rate - If you want to slow down the speed at which the book is read, toggle this on.
Read to me. Press or click on this button to have the book read to you.