1. Make sure the 'sinatra' gem is installed. 2. From the command line, you can start the server by 'ruby main.rb' 3. If you have the 'shotgun' gem installed, you can instead run 'shotgun main.rb' 4. ctrl+c to stop the server please keep in mind that Sinatra apps in Nitrous.io need to be restarted every time a change is made to any code