After cloning the repo, you will need to install Ruby libraries. It's recommended to use an environment manager for this in case you will run multiple projects with different dependencies.
Please check rbenv or rvm for this. Note that you can also use system Ruby for development, but make sure you're on a safe and stable version. (>= 2.4.*)
Then you just use the bundler gem to install library files:
$ gem install bundler
$ bundle install #on project root directory
And start the server:
$ ruby web.rb
Check the port shown on the console (probably 4567) and navigate there on your browser, like http://localhost:4567 .
This app does not use a conventional database, it utilizes Google Spreadsheets for the storage of data. To access the content, you will need to authorize your Google account with this app and keep the auth file on the development filesystem. It is ignored by the git repo so you'll need to do it again on the production server.
Easiest way to do it is to open an interactive console with the app loaded:
$ tux
and run the method to update the contents from the spreadsheet:
>> fetch_content
On this step the google_drive gem (Ruby library) will provide a link to
authenticate. Just open and follow the steps to get the auth token and paste it
into the interactive console. A file called stored_token.json will be created
in project's root folder and further content updates will work smoothly.