Miles Chapter 1 on Computers and Programs makes a good introduction and gives context. Read for the grounding it gives.
The chapter makes some reference to Microsoft, the original creator of C#, and its Visual Studio software development environment, which works only on Windows machines, and costs a lot if you are not a student. The optional text by Lewis discussed Visual Studio at some length. The next section of these notes will introduce an alternative to the Microsoft environment: Mono, which is free, open-source software that makes C# available for multiple platforms: Windows, Mac, or Linux machines.