file type help

Forgive me if I get some of the jargon wrong, I’m relatively new to PC’s. In Win 98SE under Folder Options you can assign a particular application to open a specified file type. However, it seems that a given file type may be opened by multiple applications. MP3’s, for example, open under both Real Player and Media Player. Where can I find a list of what applications are associated with what file types and the associated file extensions. Far from a pro’s question, but any help would be appreciated. Thanks.