To we understand the concepts, let's create a sinatra app, that will simple calculate the inputs.
You're not limited by any structure files. Do what you learn in the last few days.
Create the base app, adding the Gemfile (including the lock one), the rb files following the "rackup way", with a route /status
that should returns a simple text "OK". Also add the rspecs for that. The server should be able to run with "bundle exec rackup". The rspec should cover the /status
.