import/using a namespace depends on which language you have chosen to create your application.
The Import statement is
VB.NET specific.
The using statement is
C# specific.
for example if you want to use the namespace
System.Data.SqlClient
in your application then:
In C# you write:
using System.Data.SqlClient;
In VB.net you write:
Imports System.Data.SqlClient
They both perform the same thing, but they are specific to that particular language.
hope it helps :)