I'm sure any number of us can give a long explaination about the archived files and what you should do with them, but first check out [url]http://technet.oracle.com/doc/oracle8i_816/server.816/a76993/toc.htm[/url] so you can get a better understanding about what the files actually are and what their purpose is.

They are the archived redo log files, the gist is that they are used for complete recovery up until the point of failure, and you need to keep all those which are applicable to your database (basically those newer than your last backup)