>> an ISO image merely means that the image is bootable.
Not exactly... it doesn't have to be bootable. ISO just means the image is in a particular format, and this type of format is known as "ISO" - it's a standard format that most CD burning proggies understand. As compared to .NRG which is Nero's proprietary image format, etc.
Floydy, an image of a CD means it's a "carbon copy" of the CD, including all file tables and data etc.... On its own it's not much use but once you burn it to CD it's like making a clone of the original disc.
In Nero you just go to Recorder / Burn Image, browse for the .iso file and burn it. Probably the easiest burn operation to do in Nero actually