Click on File
Click on Burn Image
It will default to the Nero image extension choice - so you won't "see" your .iso file. In the drop-down box chose the other option - all files. NOW you will see all files INCLUDING your .iso file.
99.999% just accept the default selecion that Nero chooses for data type - and burn away.
I have done this at home, at work, at friends - as have many others. If you actually READ the instructions (they are also on Nero's page - go figure) and follow them, it will work.