The Compare Properties feature page allows visitors to your site to compare the different features that the properties offer. To activate this features you just need to create the Compare Properties page.
How to create the Compare Properties page
In your left sidebar navigate to Pages > Add New to create a new page and from the Page Attributes box located in the right sidebar select Template: Compare Properties and Publish the page.
Enable compare properties on listing page
Navigate to Theme options > General as displayed in the image below and locate the Compare (4) option to Enable/Disable property compare button on the listing pages.
Based on your settings you should see the elements highlighted in the image below to compare properties.