Before beginning, generate the code required to implement your button: see here for info (part 1).
Log in to your Webself editor, and visit the page you want to add the book now button to.
Click "+ ADD", then select the "Script" in the Tools Sections.
This screen will appear:
From the code generator, copy the head tag script and paste it in the "Content code between <head> and </head> tags" section.
From the code generator, copy the body tag script and paste it in the "Content code between <body> and </body> tags" section.
From the code generator, copy the button tag script and paste it in the "Code Content" section.
Click "Save".