If you are using Joget Enterprise or Professional version, use this form element Calculation Field to add two or more fields. 

If you are using Joget Community version, you hv to use Custom HTML and Javascript ( example here ).

Please help with this custom HTML as I have to display the addition of this duration of experience and validator whether it is more than or equal to 5 years.

CODE:

<script language="JavaScript" type="text/javascript">

for (int i = 0; i < rowLength; i++){
$('input[name="exp"]').change( function(){
d1 = $('input[name="exp"]');
var ex =0;
ex = ex + d1;

function calcDate(ex,d1) {
var diff = Math.floor(ex.getTime() + d1.getTime());

var years = Math.floor(diff/31536000000);
var months= Math.floor((diff%31536000000)/2628000000);
var days = Math.floor(((diff%31536000000)%2628000000)/86400000);
var msg = years + " years ";
msg += months + " months ";
msg += days + " days " ;

return msg
}
}
a = calcDate(ex,d1)
$('input[name=field8]').val(a);
});

</script>