RingCentral in ASP.Net Web Application

We are software development company and one of our client want to integrate RingCentral in our CRM application developed in ASP.Net. How we can integrate RingCentral in our web application for outgoing and incoming calls, queue handling and SMS integration. If we can get integration documentation for implementing RingCentral, any API documentation, sample code in .Net for implementing the above mentioned features and Steps to test the implementation will be great.

Looking forward for the reply.