Ubuntu installs printer automatically, if they chose non-free software during installation. For newbies we tend to think non-free cost. Click System ->- Administration -->-- Software Sources, on first tab check all 4 boxes(non-free included), 2nd tab uncheck cdrom, close.
Open terminal sudo apt-get update or sudo aptitude update
sudo apt-get install hplip-cups.
If sudo doesn't work you need to edit "/etc/sudoers" file.