Copy the code snippet under the part that says '1. Copy your code here' (i.e. the code snippet that starts "<script..."), then...
In your Zenfolio account, click ‘Website’ > ‘Built-in Pages’ > then click ‘Customize’ on whichever page you’d like to add the indemandly button to (e.g. ‘About’, ‘Blog’) > ‘Site Settings’ > ‘About message’ > then click 'Source' and paste your indemandly code snippet into the text box. Hit 'Apply'. Done!