The first lines of Listing 6 and Listing 7 are optional shorthand
statements for declaring that the application uses one or more
classes in the DirectoryServices namespace. In plain English, if
you don't include these optional statements in the code, you would
have to use longhand for writing each line of code. For example,
on the first lines of Listing 3 and Listing 4, you would have to
change DirectoryEntry to System.DirectoryServices.DirectoryEntry.
The Module keyword in Listing 6 and the class keyword in Listing 7specify names of code blocks, and the surrounding brackets
define code in the blocks. The Sub keyword with the Main() parameter in Listing 6 and the static and void keywords with the
Main(string\[] args) parameter in Listing 7 specify the starting
points (in programming terms, the entry points) for the code in the
applications. For more information about this surrounding code,
see the Visual Basic .NET and C# Programmer's Reference guides
in the Microsoft Developer Network (MSDN) Library.