The query feature requires a TEMPLATE object in the CLASS object of your LAYER definition. The value points to a html fragment using MapServer template syntax.

Example MapFile fragment:

LAYER
  NAME Parcel9
  TYPE POLYGON
  STATUS OFF
  DATA Parcels/area09_parcels
  CLASS
    STYLE
      OUTLINECOLOR 128 128 128
      COLOR 153 205 255
    END
    TEMPLATE "templates/Parcels/area09_parcels.html"
  END

  HEADER "templates/Parcels/area09_parcels_header.html"
  FOOTER "templates/Parcels/area09_parcels_footer.html"

END

Example Template:

<tr>
  <td>[lrn]</td>
  <td>[PIN]</td>
</tr>

The [lrn] is a special keyword that indicates the resulting line number which starts at 1. [PIN] is the name of a feature attribute.