The book is currently broken down into several sections and is intended to be read sequentially.Getting started will show how to install and get started with Ruby in your environment.Basic Ruby demonstrates the main features of the language syntax. TheRuby language section is organized like a reference to the language.Available modules covers some of the standard library.Intermediate Ruby covers a selection of slightly more advanced topics. Each section is designed to be self contained.
These are parts of Ruby that you have available (in the standard library, or via installation as a gem).To use them you typically have to require some filename, for examplerequire 'tracer' would make accessible to you the Tracer class.
You can see a list of basically all the (std lib ruby) modules available in theruby source andlib readme. There are a several more modules available in the std lib, which are C based extensions. You can see their listhere.
BigDecimal gives you a way to have arbitrary precision Decimal style numbers. Never succumb to rounding errors again!
Debugger gives you a way to step through debug your Ruby code.
Distributed Ruby (DRb) gives you a way to make remote procedure calls against objects in a different VM.
mkmf is a utility used to generate makefiles for ruby extensions.
Mutex gives you a way to control thread concurrency.