I'm going to install Ubuntu version 12.04 but I don't know how much space on an empty dvd-r or cd-r I would need. Does anybody know? Also can you install Ubuntu directly on your hard drive? please help!
The standard desktop CD install image is just under 700 MB, the DVD image is at most 1.6 GB. A standard 700 MB or higher blank CD or any blank DVD will do (you can also use a USB thumb drive).
You'll need to boot from your chosen install media (CD, DVD or USB drive) to install.
If you haven't already read the official instructions I would highly recommend you do so.