asp.net-core-mvc

I often find these two names on the Internet. Are these different technologies or just two names for the same framework? And if there is a difference, please explain it.

I'm trying to figure out how to add roles and assign them to users in Razor Pages 2.1. I need to create an administrator role ... tunately, this approach in Razor Pages did not work for me. Tell me how you can create and assign roles in Razor Pages 2.1.