Even though Rahul's answer is correct, I'd suggest a slightly different approach. After you've installed apache2 and phpmyadmin using apt-get, do this:

sudo ln -s /etc/phpmyadmin/apache.conf /etc/apache2/conf-available/phpmyadmin.conf
sudo a2enconf phpmyadmin
sudo service apache2 restart

The benefit of my approach is that you won't have to resolve configuration conflicts when you upgrade Apache. You need Apache 2.4 though, which is included in the repositories of Ubuntu 14.04.

Edit: Also, the message about the fully qualified domain name has nothing to do with this. Don't worry, unless you're actually setting up a site which needs a domain name.

Assuming you followed those installation instructions to the letter, phpmyadmin should at least be installed on your computer. However, Apache configuration needs to be added for it to work.

When you installed phpmyadmin, it should have automatically set up its configuration for Apache, making it accessible at http://localhost/phpmyadmin/ (it's possible you may need the trailing slash?).

However, in case it didn't, you can re-run the initial configuration step with the following command:

sudo dpkg-reconfigure -plow phpmyadmin

When changing Apache configuration, it should usually restart Apache automatically, but in case it doesn't, you can always restart Apache with:

sudo service apache2 reload

(Some changes require restart instead of reload).