Ruby is a newly popular interpreted language from Japan. Unlike Python, which is a general-purpose language used in scientific computing, web, game, and application development, Ruby is as of yet mostly used for building server-side backends of websites.
Otherwise, Ruby is as powerful as any other language, and everything that can be computed, can also be computed in Ruby.
You should start by reading this poignant guide to Ruby.
If you are already proficient in another programming language, like Python, you can go over the faster Ruby in 20 minutes guide, and/or Ruby Koans.
Now, complete (at least) one of these courses: