Need details discussion on configuration settings using useconfiguration(config)

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ASP.NET-Core

var config = new ConfigurationBuilder()
.AddCommandLine(args)
.AddEnvironmentVariables(prefix: "ASPNETCORE_")
.Build();

var host = new WebHostBuilder()
.UseConfiguration(config)
.UseKestrel()
.UseContentRoot(Directory.GetCurrentDirectory())
.UseIISIntegration()
.UseStartup<startup>()
.Build();

host.Run();


Hello,
I am new learner in asp.net.Can you please explain line by line code.What is the purpose of each and every line of the code.

Specially I need a details discussion on configuration setting
var config = new ConfigurationBuilder()
.AddCommandLine(args)
.AddEnvironmentVariables(prefix: "ASPNETCORE_")
.Build();

with regards,
Subrata
Thank you

What I have tried:

I try to find the solution from asp.net core 2.0 Microsoft document but I am unable to understand.