OpenID Connect Playground
One of the best ways to learn the OIDC flow is to see it in action. This is also an excellent resource to troubleshoot issues with OIDC integrations - it allows you to see the tokens flowing between the browser, the relying party, and the identity provider right in your browser. This tutorial leverages the OpenID Connect Playground debugging tool provided by Auth0 / Okta (they may be competition, but they have great resources for developers!)