Angular app with .Net core backend

This might be a stupid question.
I have an Angular app with .Net core back end. I want to integrate SSO using OKTA OpenIdConnect. I had our admin create a new custom SPA application in OKTA and added the users and I got the ClientID and everything. I don’t know where to go from there
I am following this blog But it is not helping.
I don’t want the users to enter their login credentials I want a straight sign on when I launch the application. What do I need to configure OKTA to do SSO? How can OKTA know which user is trying to access the application in order to authenticate him/her?
do I need to pass in user id from the .Net app? the angular app doesn’t know which user is logging in to app so how can I tell OKTA service that it is me who is trying to login?