To hide a field (or field Heading), right-click the field, format feild, Common Tab. Go into the x+2 button next to suppress and enter:
isnull{yourTable.yourField} or {yourTable.yourField} = ""
To hide a section, go into Section Expert, select the section on the left, Go into the x+2 button next to suppress and enter:
isnull{yourTable.yourField} or {yourTable.yourField} = ""