I have heard many times the word assemblies. Still I don't know what they are and its uses in programming language.
Most of your questions are for c# so here is the link for .net Assembly
In the .NET framework, an assembly is a compiled code library for use in deployment, versioning and security. There are two types: process assemblies (EXE) and library assemblies (DLL). A process assembly represents a process which will use classes defined in library assemblies. .NET assemblies contain code in CIL, which is usually generated from a CLI language, and then compiled into machine language at runtime by the CLR just-in-time compiler.