I have answered a lot of questions about C# and the .NET framework. I can understand why it is confusing. When I first began programming against .NET I was completely confused about what .NET even was. I thought it was just because it was my first real programming experience, but it turns out that a lot of people don't know even the simple details about C# or .NET. Here is the verbose answer I gave on a question recently:
.NET is a framework. What that means is that the .NET platform contains libraries of existing code and architecture from which all applications utilizing it build from. So rather than pouring a new foundation for every house, you already start off with a solid one that has been perfected and improved upon over time. In addition to a starting foundation, the framework serves as a sort of toolbox of existing code that saves you from reinventing the wheel every time you need certain things.
For instance, winforms is an established foundation from which to build windows applications with a rudimentary user interface simply by going to file > new project. You would have to interface with GDI yourself to generate windows forms and user interface if this library of existing code was not there to support you.
C# is simply a programming language. One specifically written with .NET in mind. In fact, most of the .NET framework is written in C# (if not all of it). It's syntax is simply the next progression of the C language, thus transitioning from C++ to C# shouldn't be too difficult. It's a paradigm shift with a lot of things, but at least the syntax is often familiar. Any .NET language is usually compatible with other .NET languages. For instance, I could write a class library in Visual Basic, and you could use that compiled library in your C# program.
Because .NET is a framework, the code you reference in it does not get compiled into your program, rather a reference to code in the framework is all that gets compiled. This means that clients running your program must also have the .NET framework, albeit a stripped down version. They don't need all the development tools that you need so their .NET framework download is a little smaller. Clients running Windows Vista/7 don't need to worry about anything; it's included with their OS. Only certain users running XP would even have to worry about downloading the framework, and most programs accurately detect the requirement and inform the end user to go download it.
All versions of Visual Studio are simply tools to help you build applications and better utilize the .NET framework. I would never recommend coding in any .NET language without at least the express (free) edition of visual studio. Intellisense alone is worth it. That said, it is definitely possible to code something in .NET without the Visual Studio IDE. You could open up notepad right now and write a C# program, compile it with the free compiler, and run it. While Visual Studio 2010 is pretty amazing, and uses the new WPF platform to run, 2008 will serve you just as well. 2010 is optimized for .NET 4 but works just fine when targeting previous versions of .NET as well.
- .NET is a coding framework.
- C# is a language built to take advantage of .NET. NOTE: Visual Basic is also a .NET language and choosing between C# and VB is simply a matter of preference.
- Visual Studio is a tool to help you in coding for .NET.
That is how they are all related.
If you are interested in learning C# I have put a very basic beginner's tutorial togther. Check it out.