If you're using the standard single property actions template, once the Property Shortlist add on is activated, you'll automatically get the add/remove button appended to the list of available actions.
Clicking the 'Add To Shortlist' button for the first time will add the property in question to the users shortlist and update the text of the button to 'Remove From Shortlist'. It does this by making an AJAX request, therefore making the process smooth and reducing the need to do a full refresh of the window. Clicking the button again will remove the property from the shortlist and restore the button text.
Behind the scenes the AJAX request appends chosen properties to a cookie called 'propertyhive_shortlist'. This cookie is set to be active for 7 days and will expire after this time if the user does not return to the website and update their shortlist in anyway. That is unless a user is logged in, in which case it will save any properties to their account which will appear as a new tab when logged in and using the [propertyhive_my_account] shortcode.
There are two available shortcodes available with this add on:
Place the 'Add To/Remove From Shortlist' action button anywhere you like with this shortcode.
Adding this shortcode will output a list of properties that are currently shortlisted by the user.