Okta App and IDP

I am working on SAML2.0 authentication in asp.net. I have configured the App and IDP in Okta. My question is where we map App and IDP(relationship)? and how to validate the certificate in asp.net?

It should be the metadata generated by the app from link under sign on tab that is configured in the asp.net config i.e. Identity Provider Single Sign-On URL, Issuer and Certificate