This tutorial guides you through creating a Ruby on Rails conference call application using the Nexmo Voice API. To accomplish this, you need to create a new Rails application, expose it externally with ngrok, set up your Nexmo account and phone number, link your application to your phone number, define your Rails Controller actions and routes, and run your application. The tutorial provides a comprehensive walkthrough of each step, including setting up ngrok and defining the necessary NCCO instructions for the conference call. Once you complete these steps, you can make calls to your Nexmo-powered conference call and invite others to join in.