how to create file .dll from .vb

I don't understand how to create file hello.dll from file hello.vb and what mean's "C:\>vbc /t:library hello.vb" in the part 2.1:

"

Example 2-1 contains the listing for our "Hello, world" component. It contains a single class named Hello with a single method named Write. Save the listing to a file named hello.vb. The rest of the chapter will use this listing as a foundation of discussion.

Example 2-1. The "Hello, world" component

Option Strict On

Imports System

Namespace Greeting

Public Class Hello

Public Sub Write(ByVal value As String)

Console.WriteLine("Hello, {0}!", value)

End Sub

End Class

End Namespace

The Visual Basic .NET 
command-line compiler is a program called vbc.exe 
that should be in your path once the .NET Framework is installed. All examples 
in this book assume that the example code exists in the root directory of your 
hard drive. This assumption is made to improve readability. If the code is not 
in your hard drive's root directory, you need to specify a fully qualified 
pathname to the compiled file or compile from the directory where the source 
code is located. With this in mind, you should be able to compile Example 2-1 to a dynamic link 
library (DLL) as follows: 
C:\>vbc /t:library hello.vb
The /t: 
option is short for target, which can be one of the following values: 


exe 

A console application. If the /t switch is omitted, 
this is the default value. 
winexe 

A Windows executable.
library 

A DLL.
module 

A module. This value is similar to a .lib file in C++. 
It contains objects but is not an executable. 
As a default, the compiler gives the output file the same name 
as the file being compiled. Here, a file named hello.dll is produced. 

"

can you help me???

thanks in advance!