Gauri,
You will get values of clientID after registering your website/portal in Gluu Server.
'registering client' is another side of coin of doing Trust Relationship for SAML.
For OpenID Connect setup, you need to perform this client registration.
You can register your client ( aka. RP / website / portal )in Gluu Server either using dynamic registration or manual registration.
Check [this](https://gluu.org/docs/integrate/ubuntu-installation/) documentation...here we are showing how you can 'register' your RP with Gluu Server.