how to use jquery ajax in php

Short answer for @plmexico79: PHP receives form fields by their HTML name attributes, not by id. As @pritaeas said, giving inputs an id makes client-side selection easier, but the server reads $_POST['fieldname'] where fieldname is the input’s name. For quick AJAX submissions use a form id, give each input a name, and let jQuery serialize the form.

Example HTML (note the name attributes):

<form id="myForm">
  <input type="text" name="email" id="email">
  <input type="password" name="password" id="password">
  <button type="submit">Send</button>
</form>

Use jQuery to serialize and post the form (client expects JSON back):

$('#myForm').on('submit', function(e){
  e.preventDefault();
  $.ajax({
    type: 'POST',
    url: 'process.php',
    data: $(this).serialize(),   // uses input name attributes
    dataType: 'json',
    success: function(resp){
      if (resp.success) { /* success flow */ }
      else { /* display resp.errors.fieldname messages */ }
    }
  });
});

Server-side skeleton (return JSON errors):

<?php
header('Content-Type: application/json');
$errors = [];
if (empty($_POST['email'])) $errors['email'] = 'Email required';
if ($errors) echo json_encode(['success' => false, 'errors' => $errors]);
else echo json_encode(['success' => true]);

Troubleshooting notes: confirm inputs have name attributes; check the browser Network tab for the AJAX request and response; set dataType: 'json' so jQuery parses JSON; ensure PHP sends Content-Type: application/json and no stray whitespace before <?php. For file uploads use FormData (see FormData docs) and send with processData: false, contentType: false. See the PHP $_POST manual and the jQuery .serialize() docs for details: PHP $_POST · jQuery .serialize() · FormData (MDN).