What to do with a Ruby git repo depends on what is in it, and usually described how to use it by the README.
In this case, the repo is for a gem, and it does not contain any Rails server examples or Rails projects.
Unless you have a specific need to use the github version, you should just use the version from rubygems.org
Ignore your cloned item for now, and add the gem to your own Rails project's
gem "amaze_sns", "~> 1.3.0"
If you want to use this service as part of a Rails application, and don't yet have one, then you will need to create a new one. Other repos may contain example applications to get you started quickly - just not this one.
When you run
bundle install or
bundle update, Bundler will sort out a suitable copy of the gem for you.
The repo's examples here https://github.com/cheeyeo/Amazon-SNS-Ruby/tree/9cb8727ae104c39f44e795eef24b2012c3c7885a/example give some idea of how to use the gem in practice. You may be able to type that code into the Rails console, if you first do
gem install amaze_sns
to add the gem to your system Ruby (you probably don't need a full project started to do that testing)