Help for beginner with iso files

[Golfbally]

Hi, I am a total beginner at this stuff. I have loads of iso DVD's on a hard drive that I usually play through a request movie server on TV. Want to be able to play on laptop / computer as well. Downloaded latest VLC media player, then do the following;
Media>Advanced Open file
Add file (currently z: on network)
Highlight the iso file , then play

Nothing happens, so obviously doing something wrong. Anyone kind enough to explain what I have to do ?
Please imagine you are teaching a 5 year old, as that is the extent of my computer knowledge.
Having said that my own 5 year old would probably do better so if no one can help, I will ask him......