JQuery :: Insert Data In Database Mysql With Php?

I'm triyng to use the $.ajax jquery function to insert some dates in a database, using php.I have the page that insert the data called : sign.php and in the page I have the form, and the ajax scritp.

$("#submit_sign").click(function(data){
$.ajax({
type: "POST",
url: ("sign.php"),

[code]....

if I use the page without ajax it works, if I use the script jquery it works but doesn't insert the dates in the field, it send only white field. can't pass the variable POST beetween the ajax script and the php script.