Inside /config/database.yml, enter your database details:

development:
  adapter: mysql
  encoding: utf8
  reconnect: false
  database: shoutbox_development
  pool: 5
  username: root
  password:
  socket: /tmp/mysql.sock

You will likely only need to change the username and password.
If you are deploying to a production server, configure those details, also.

From your command line, navigate to the shoutbox's directory and run the two commands below. The first will create your database, the second will set up the table:

rake db:create

rake db:migrate

Start the server with ruby script/server and try it out!