Configure Gmail , Yahoo, Rediffmail account under Okta identity

How can I make my Gmail , Yahoo, Rediffmail email service accounts to be configured under Okta directory, so that with single sign on I can login to all these email accounts, once I logged into Okta.

I know how to configure Okta IDP through documentation provided in Okta idp site for developers.
But could you please let me know in brief , what kind of changes I need to do at service provider end i.e in my Gmail, Yahoo, Rediff account.

Please help.

Also Can I configure a .net application into Okta idp site , which running on my local machine inside local IIS, which is not hosted in internet. So that I can test SSO for application running on my local machine, and I can do required modifications at service provider side.