Summary
Visual Studio is powerful, it is so powerful that you will eventually rely on it completely, without fully understanding the backend mechanism. This entry list 3 types of DotNet core external reference solutions. Without the interference of VS. by bare hand typing.
Type 1. reference to NuGet packages - PackageReference
Type 2. Reference to project
When using project reference, it is no need to include dependent packages in your main project (referrer project).
Type 3. Reference to external DLL
Please do remember to include all dependent packages in your main project.
