using

System.Console.WriteLine("Hello World");

Namespaces are used to organize classes. In the above example, System is a namespace, Console is a class, and WriteLine is a method.

The using keyword can be used to make it so the namespace is not needed:

using System;

Console.WriteLine("Hello World");

Your csproj may have even configured some implicit "usings":

<ImplicitUsings>enable</ImplicitUsings>

scope

Declaring a namespace can help you control the scope of class and method names in larger programming projects.