A Featuring Artist is a guest artist or secondary performer that you want to call special attention to. (ie: Hence the word, Featuring). You should not submit members of the band as Featured Artists.
Featured Artists should be used sparingly, and only in the case where you want to highlight a guest artist. Generally, there really should never be more than four featured artists on a track. If you have more than four featuring artists, then they probably are not really featuring artists and should simply be listed as additional contributors with the specific role that they played on a track (ie: Drums, Guitar, etc).
*Some stores will append the Featuring Artist to a track's title, but this happens automatically and so you should never enter the Featuring Artist in a track's title yourself.