Knowledge Is Power

It is an object oriented programming language. it contains a systematic collection of classes and objects.
please read Object oriented term better.
Visual Basic .NET comes with thousands of built-in classes which are ready to be used.
So it is easier to write in VB.net then Visual Basic. once we have learn how to use .net framework.
Creative Calligrapher dot com has answered every thing. But the Question of Why we use it lies open. I will try to fill in the Gap.

If you are appearing in a VB exam you will use it , if you are interested in earning money you will use it, if you are interested in just programing you will use it, if you are a VB programmer you will use it, if you have a lot of time in your hand you will use it, now the main reason if you like the kick of success (virtually) you would use it. VB is a relatively easy language to learn and sovling tricky problems gives a feeling of success (quick and deserving success), so just for the sake of it you can use it

Vb.net is a framework. means simply it is a collection of large library to solve different programming needs when a programmer wants to write a software. A library is not of books but of small different collection of code .

Vb.net is a Visual Basic in .net framework. means one who knows Visual Basic then VB.NET is an extention of Visual Basic

There have been nine versions of Visual Basic up to the current version. The first six versions were all called Visual Basic. But in 2002, Microsoft introduced Visual Basic .NET 1.0, a completely redesigned and rewritten version that was a key part of a whole computer software revolution at Microsoft. The first six versions were all "backward compatible" which means that later versions of VB could handle programs written with an earlier version. Because the .NET architecture was such a radical change, any programs written in Visual Basic 6 or earlier had to be rewritten before they could be used with .NET. It was a controversial move at the time, but VB.NET has now proven to be a great programming advance.
One of the biggest changes in VB.NET was the use of a object oriented software architecture (OOP). (Tutorials on the site explain OOP in much more detail.) VB6 was 'mostly' OOP, but VB.NET is totally OOP. The rules of object orientation are recognized as a superior design. Visual Basic had to change or it would have become obsolete.

In the beginning, there was BASIC and it was good. Really! I mean, really the beginning. And yes, really good. BASIC ("Beginner's All purpose Symbolic Instruction Code") was designed as a language to teach people how to program by Professors Kemeny and Kurtz at Dartmouth College w-a-a-a-y back in 1963. It was so successful that soon a lot of companies were using BASIC as their programming language of choice. In fact, BASIC was the very first PC language because Bill Gates and Paul Allen wrote a BASIC interpreter for the MITS Altair 8800, the computer most people accept as the first PC, in machine language.
Visual Basic, however, was created by Microsoft in 1991. The main reason for the first version of Visual Basic was to make it a lot faster and easier to write programs for the new, graphical Windows operating system. Before VB, Windows programs had to be written in C++. They were expensive and difficult to write and usually had a lot of bugs in them. VB changed all that.

It's a computer programming system developed and owned by Microsoft. Visual Basic was originally created to make it easier to write programs for the Windows computer operating system. The basis of Visual Basic is an earlier programming language called BASIC that was invented by Dartmouth College professors John Kemeny and Thomas Kurtz. Visual Basic is often referred to using just the initials, VB. Visual Basic is easily the most widely used computer programming system in the history of software.

The evolution of HTML has essentially stopped. Instead, HTML is being replaced by a new language, called XHTML. XHTML is in many ways similar to HTML, but is designed to work with the new eXtensible Markup Language, or XML, that will soon serve as the core language for designing all sorts of new Web applications, in which XHTML will be only one of many "languages." But, XHTML is designed to work with these other language, so that different documents, in different languages, can be easily mixed together.

Today, the Internet is positioned to be an international mechanism for communication and information exchange, the precursor of a global information superhighway. For this vision to be realized, one important requirement is to enable all languages to be technically available via the Internet, so that when a society is ready to absorb Internet technology, the language capability comes prepackaged. This is a nontrivial multilingual-information processing problem. To appreciate the extent of this issue, it is enough to know that few years ago, English was the native language of 80% of web users. Today, English is the mother tongue of less than half of web users. However, statistics show that the language of about 80% of web sites is English with only about 8% could be classified as multilingual 

From the numbers above, making a website universally usable is an important issue and ignoring it may lead to groups of users suffering isolation, rather than enjoying the true interoperability alluded to by the very name of the World Wide Web. However designing websites in languages other than English or multilingual websites confronts designers with many requirements. These requirements generally fall into three categories: data representation, data display and data input requirements . This paper studies these requirements, gives general recommendations for meeting them and provides a list of guidelines for web pages designers. It also gives examples of successful websites implemented in different languages.