also see http://webwork.maa.org/wiki/AnswerFormatHelp
http://webwork.maa.org/wiki/AnswerHints
If the help you want is not in AnswerFormatHelp then something like the following will work if you know the help file name
and it is located in the htdocs/helpFIles folder:
return knowlLink($display_text,
url=>$envir{'localHelpURL'}.$infoRef);