The dialog is diasplayed after you selelct Customized from the drop-down list of the Show Fields property, which is in the Hint category of the chart pater of a heat map in the Report Inspector. It allows you to select fields to show as hint. See the dialog.
From the Resources box select a field and then click 
to add it into the right box. Repeat this to add more fields. The names of the selected fields will be displayed in the value text box of the Show Fields property, separated by ",".
OK
Applies the changes and closes the dialog.
Cancel
Does not retain any changes and closes the dialog.
Help
Displays this help document.
