After you have created your HTTP Listener and by example used it in a Logic App, you want to test it to validate if it is accesable.
Go to Browse
Click API Apps
Click the link under Host
Click the link under URL
Change Http:// to Https:// in the address bar of your browser and put the operation (if defined) at the end. Your link should look something like this:
Test your URL with a tool like SoapUI or Postman.