Administrative Access
By default, the root user cannot log in under Ubuntu. This is a reasonable default, and you probably should leave it that way. All admin access should be done with sudo:
sudo synaptic
sudo emacs /etc/apache2/sites-enabled/000-default
sudo sh # if you're doing a lot of admin stuff
Installing More Software
After you have installed Ubuntu, you may find that there are more packages that you need to install. This is quite easy in Ubuntu.
If you prefer a graphical interface, you can use Synaptic. This can be started from the Systen/Administration menu, or with the synaptic command. Click “Reload” to refresh the package list, select/deselect packages, and click “Apply” to install.
The command-line tools are also easy to use. To install packages, just type a command like:
apt-get install mysql-server
All required packages will automatically be downloaded and installed. Any critical questions/messages will be asked/displayed (with either apt-get or Synaptic).