Support for the Ruby 2.1 series ended on March 31 2017. See here for details.
The Ruby syntax is large and is split up into the following sections:
Numbers, Strings, Arrays, Hashes, etc.
Assignment and variables
Method and method argument syntax
How to call a method (or send a message to a method)
Creating modules and classes including inheritance
Exception handling syntax
Precedence of ruby operators
Use and behavior of the experimental refinements feature