What exactly is an Assembly in C# or .NET?

Question

Could you please explain what is an Assembly in C# or .NET?

1. Where does it begin and where does it end?
2. What important information should I know about

Answer 1

Here's another explanation of the make up of .NET Assemblies, a mini-quote:

The .NET framework consists of the concepts of modules, assemblies, which both store metadata and manifest information. An assembly can contain multiple modules. Visual C# only ever creates one module which is turned into an assembly by the C# compiler (csc.exe), but an assembly can link many .NET modules together via the assembly linker (al.exe) command-line tool. For example each of your source code .cs files could be compiled into a module and linked together to form an assembly - an assembly is just a collection of modules and resources. One of these modules, however; must contain manifest metadata (see below) information for the assembly to be understood by the CLR.
....
Having created a new .exe or .dll inside VS.NET you see your file appear inside your bin folder. Opening it in notepad will give out gibberish, or even inside a hexadecimal editor without knowing the structure of the file, you need a tool like ildasm.exe or CFF explorer to make meaning from it. The structure of the assembly is as follows:

PE header
CLR header
CLR metadata
CLR
IL code
Native data