How it worked for me:
FYI: Instead of
sudo -u postgres createuser chris -s
sudo -i -u postgres createuser chris -s
Also, in the config/database.yml file, under pool:5, add
host: localhost username: pguser password: pguser_password
(pguser) + (pguser_password) is the username and password you created. Also add this to the "test" envrionment section.
And finally if
rails server doesn't work, if you're using a Virtual Server like Digital Ocean, use:
rails server --binding=server_public_IP
where (server_public_IP) is the server's IP address. Then use
http://server_public_IP:3000 in your web browser.