Getting started with rails, you should read this:
3.2 Creating the Blog Application
Rails comes with a number of scripts called generators that are designed to make your development life easier by creating everything that’s necessary to start working on a particular task. One of these is the new application generator, which will provide you with the foundation of a fresh Rails application so that you don’t have to write it yourself.
To use this generator, open a terminal, navigate to a directory where you have rights to create files, and type:
$ rails new blog
This will create a Rails application called Blog in a blog directory and install the gem dependencies that are already mentioned in Gemfile using bundle install.
$ cd blog
Now you are ready to use
rails generate ... etc …