I want write "Hello World" with ASP.NET Core

its pretty easy:

mkdir webhello
cd webhello
dotnet new web
dotnet run

you will end up with a program.cs that looks like:

var builder = WebApplication.CreateBuilder(args);
var app = builder.Build();

app.MapGet("/", () => "Hello World!");

app.Run();

and a webhello.csproj that looks like:

<Project Sdk="Microsoft.NET.Sdk.Web">
  <PropertyGroup>
    <TargetFramework>net8.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>
</Project>