Talking to IdentityServer4 with an Angular SPA application for authentication/authorization receiving a token then talking to Web API
Identity Server has different flows/grant types, the one you talking about called implicit in that case Identity Server will return a jwt token so you have to be storing that jwt token on a client and then attaching that token to request header when requesting your secure webapi routes.
Official samples it is very good starting point also checkout their blog that has lots of useful info covering the topic.
Talking about the good videos on the topic here is a good one from the recent NDC conf IdentityServer4: New & Improved for ASP.NET Core also if you want to learn stuff more deeply you can checkout this pluralsignt course by Dominick Baier