How Do I make Multiple "Entry Points" in a .NET CORE app?

Question

I am new to .NET CORE but I have followed a few tutorials. The tutorials I have followed are basically "Hello World" types of programs where I make a small functional .Net Core application and I publish it. They are basically a DLL, I assume, and they run in some sort of system/container where they can run on any OS.

Even though the final product is a DLL, the code itself seems to be structured in a way where it is an actual executable application.

So how would I translate an actual C# DLL project into a .NET Core project? How would a project that is already designed to produce a DLL work in a .Net Core project?

Executables only have one entry point: static void Main.

.NET Libraries expose public methods which are all entry points in that sense.

An "entry point" in a program is where the operating system invokes an executable program file, the term does not apply to libraries. (and ASP.NET web-application files are really just libraries, the ASP.NET host just looks for certain exposed Page/Handler/Controller types). This applies to ASP.NET. Does it also apply to .NET Core? Also, when I ran my .NET Core applications, I did it from a special command line. So how would that work if I translated a DLL C# program into a .NET Core program?