In order to integrate the Diagramming API into your ASP.NET Core Web App (either MVC or Razor Pages), select Manage Nuget Packages from Project menu:

Open the Browse tab, and enter MindFusion.Diagramming.Mvc in the search field. Select the MindFusion.Diagramming.Mvc package and click Install.

Once the package is installed, you should be able to add components from the library to your UI (DiagramView, NodeListView, etc).