I think you'll find this diagram useful: [
^]. From this article: [
^].
Of course, you will also want to consider what the current MS "official" classification is: [
^].
NameSpaces are a taxonomy: they organize/classify/group different collections of functionality and data, and, you can create your own to control semantic scope, or organize your own work.
With your (deeper) level of interest in the C# language and .NET, let me recommend a book by the language creators: [
^]
The C# Programming Language (Covering C# 4.0), Fourth Edition
by Anders Hejlsberg (Author), Mads Torgersen (Author), Scott Wiltamuth (Author), Peter Golde (Author)
2010 Addison-Wesley Professional
ISBN: 9780132484718
This remarkable book includes annotations by some of the most brilliant C# programmers; many of them played a role in creating/evolving C# and .NET: Brad Abrams, Joseph Albahari, Krzysztof Cwalina, Jesse Liberty, Eric Lippert, Christian Nagel, Vladimir Reshetnikov, Marek Safar, Chris Sells, Peter Sestoft, Jon Skeet, and Bill Wagner.