One of the first things you should do after you've set up your Genbook account just as you want it, is get the Book Now Button onto your website.
You'll find the instructions and button code in your Settings (accessed via the gear icon at the top right of the screen).
Scroll down to the "Connecting" section and click "Book Now Button".
You'll have several button sizes and colors to choose from, along with some HTML code, which you will need to copy and paste into the source/code view of your site. (Simply pasting the code onto your site as though it were text will NOT work.)