OpenID Connect (OIDC) is an authentication protocol based on the OAuth2 protocol (which is used for authorization). OIDC uses the standardized message flows from OAuth2 to provide identity services.
The design goal of OIDC is "making simple things simple and complicated things possible". OIDC lets developers authenticate their users across websites and apps without having to own and manage password files. This provides the app builder with a secure way to verify the identity of the person currently using the browser or native app that is connected to the application.
The authentication of the user must take place at an identity provider where the user's session or credentials will be checked. To do that, you need a trusted agent. Native apps usually launch the system browser for that purpose. Embedded views are considered not trusted since there's nothing to prevent the app from snooping on the user password.
In addition to authentication, the user can be asked for consent. Consent is the user's explicit permission to allow an application to access protected resources. Consent is different from authentication because consent only needs to be provided once for a resource. Consent remains valid until the user or admin manually revokes the grant.