Program to convert a file that is .rar to mp3

A rar is an archive file, an mp3 is an audio file. The two are not in any way the same. What you probably need to do is download winrar and unrar the .rar.

(assuming you're in windows)

WinRAR archiver, a powerful tool to process RAR and ZIP files

Simply you can't.

RAR is an archive format and MP3 is an audio format.

You need WinRAR to unarchive the RAR file and then deal with what ever is inside.
Copyrighted music no doubt downloaded from the net ;)