Demo of WP ajax call with secure wp_nounce
Add Ajax call from javascript. You can find it in https://github.com/pvnrg/wordpress-ajax-call/blob/master/ajaxCall.js file.
Register and load Jquery to run the ajax feature in your site which is define in https://github.com/pvnrg/wordpress-ajax-call/blob/master/functions.php file.
Define a function and add_action for the same where you can write your logic of ajax call, you can find the code for the same in https://github.com/pvnrg/wordpress-ajax-call/blob/master/functions.php file.
Contact me direcly on skype for any help in wordpress tech: prganvani