Bad: submit should send data to php

i have a form that contains three options that user have to choose, and then after submit button is pressed i have to send the choice for php than the php send me back the json data

my php look like this:

$x = $_POST["x"];
$y = $_POST["y"];
$z = $_POST["z"]; 

the problem is how to make submit button send the three options to php ??

Thanks in advance.