When a call is made to your Twilio number, Twilio will ask your voice application for instructions on how to respond. Each Twilio number has a Voice Request URL parameter that you can set to your application's publicly accessible URL. You can set the Voice Request URL for your Twilio number in your account portal.
First, log into your account portal and go to your Manage Numbers page. Click on the red Twilio number that you want to assign to your application.
Once you click on the number, you will be taken to the settings page for the number. There you can edit the Voice Request URL to the URL that points to your application.
Don't forget to click Save!