I'm not sure what your question is.
If you are trying to take a text field and format it with hyphens then formula text field would be
var text PartOne = Left([SSN],3);
var text PartTwo = Mid([SSN,4,2);
var text PartThree = Right([SSN],4);
IF(Length([SSN]=9,
List("-", $PartOne, $PartTwo, $PartThree))
If he field was numeric then let me know and it would be slightly different formula