LittleNodes create virtual devices which are discoverable by Alexa when you link your amazon alexa account with the LittleNodes skill for Alexa. The LittleNodes Virtual button skill can be found in the Amazon alexa skill store.
Virtual buttons are pressed or triggerd via a web url. Ultimatly the intention of a virtual button is to trigger a routine setup in the Alexa app.
When a routine has been triggered you can either make Alexa say something or you could turn on / off other smart devices.
From the button panel you can test trigger buttons by pressing the "Trigger" button or you can simply copy and paste the URL with embedded API key in to your preferred browser.