the using statement specifies a namespace that the compiler 
should look at to find any classes that are refrenced in 
our code but which aren't defined in the current 
namespaces.

With the help of the keyword using, it is possible to 
create an alias name for a namespace or type. For example  
using con = System.Console; // Create an alias
class MyClient
{
public static void Main()
{
con.WriteLine("Hey rajesh! how you");
}
}

using keyword is used to intimate the compiler to load
supported name spaces for our program.

"Using" is a keywords that spasify to compiler adll is 
used in program

using keyword is used to intimate the compiler to load
supported name spaces for our program.