A friend tells me that he can email a file from his mac to his pc at work and use it there. My question is how does that work? Does the email program convert the file or is there a program on the pc that does it? I haven't used a mac in four years. Can someone please explain it to me?

Why not get your friend to tell you...
Can this be any more than opening an emailed file on a different computer? It is done all the time.

My friend isn't tech savy. I understand opening the email but I don't understand the attachment.

Depends on what the file is. But Office documents are openable on just about any OS, OpenOffice exists on both Mac and PC, same with MS Office. Pictures don't care what OS, neither do movies or audio.

The only time you'll have a problem is if its some file created by a program that has no equivalent on the other OS. Those are pretty rare unless you are working with specialized business programs developed "in house".

Thanks for answering my question. I do think I understand now. I've been doing some reading on microsoft's website about their sharepoint server. Also I believe office for mac would make the files compatatible. So there would be no need to convert. Thank you very much for your help. These discussions always help me to think better.