Guides on installing Ruby can be found on the main ruby site. These are collated below

If you’re on a Mac, start reading. If you’re on a Windows machine, skip to 2 below.

1. Installing on Mac OSX

If you’re using OS X El Capitan, Yosemite, and Mavericks, Ruby 2.0 is included and you don’t need to do anything else

If you’re on Window’s Skip to 2.

1.1 Check if Ruby is installated

To check if it’s installed open Terminal (you can find it on your Mac in Applications and then find the subfolder Utilities); then type the following at the command prompt

ruby -v

If you get something like the below you’re in business:

ruby 2.3.1p112 (2016-04-26 revision 54768) [x86_64-darwin15]

If the Ruby version number is lower than 2.3.1 or you don’t see something like the above, you should install or upgrade ruby. We’ll walk through this now.

The best (and personally recommended) way to install ruby on Mac OSX is to use HomeBrew and RVM. We’ll walk through this step by step below.

1.2 Install HomeBrew

First check if it’s installed, by typing in the Terminal Window

brew

you’ll probably get something like this

-bash: brew: command not found

To install, type the following

/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

Note: you might be asked to type your password in. That’s perfectly normal

1.3 Install RVM

RVM is a ‘command-line tool which allows you to easily install, manage, and work with multiple ruby environments from interpreters to sets of gems.’ It makes managing multiple versions of Ruby a breeze, as well as managing gemsets.

First, we’ll install gpg using HomeBrew, this checks the encryption and validity of the RVM download, and if you don’t have it installed you might get an error. To add it, type

brew install gpg

Then type:

gpg --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3

Now to install RVM, type

\curl -sSL https://get.rvm.io | bash -s stable

Note: you might be asked to type your password in. That’s perfectly normal

1.4 Close and Reopen

Close and reopen the terminal window. This refreshes some scripts and stuff in the background.

1.5 Install / Update Ruby

Finally, to install Ruby just type:

rvm install ruby --latest

Check that it’s installed by typing

ruby -v

1.6 Install Bundler

Bundler is the most useful gem for working on web stuff. It allows you to quickly manage all the gems (or libraries) attached to your project. We’ll use it lots, so install it by typing:

gem install bundler

2 Installing on Windows

Note: These instructions are untested, I don’t have a Windows machine so you may encounter problems! fingers crossed you don’t

First check if it’s installed open Command Prompt (you can find by searching for cmd.exe in the Windows toolbar)

ruby -v

If you get something like the below you’re in business:

ruby 2.3.1p112 ... 

If it shows any number below 2.3.1 you’ll need to install it again though.

2.1 Install using RubyInstaller

On Windows machines, you can use RubyInstaller. Download the 2.3.1 (x64) version from their site and launch it. Follow the prompts and dialogs.

Once it’s finished. Close and reopen any Command Prompt windows, then type the following:

ruby -v

You should see something like the below

ruby 2.3.1 ... 

2.2 Install Bundler

Bundler is the most useful gem for working on web stuff. It allows you to quickly manage all the gems (or libraries) attached to your project. We’ll use it lots, so install it by typing:

gem install bundler

If you get an error you might need to do the following. Type:

gem sources -r https://rubygems.org -a http://rubygems.org