This is probably specific to the actual program you're trying to run. Contact support for the company/individual that created the software; I'm sure they'll be happy to assist you in getting it running.

Mounting is where you can open an .iso image as if it was a disk in the drive, without having to physically burn it.

Burning is physically burning the image to a cd.

Burning an .iso image is NOT the same as burning a file. The .iso image its a copy of a disk, "inside it" could be many hundreds of files and directories, for example. So dont just burn the .iso to a disk as a file, you need to burn it as an image. Nero etc... has a mode for this, dont know about macs OSX.

And please, dont be a software pirate (and dont bring it up again here)