Well what can I say, if is Input file name, and you allready worked out that of is the output file.
[khakisample]dd if=/dev/cdrom of=/cdrom_image.iso[/khakisample] more »
Here are a collection of Mini-HOWTOs some of which are too short even for that grand title. I keep them around as it is easier to remember where to look these up that to remember the content of the mini-HOWTO