What is the diff between do_action and add_action in wordpress ?

1. The do_action function finds out about the functions it should include by a sibling function named add_action, which creates a list of all functions. You can thing of add_action  as the boss and do_action as the worker. This function, like its sibling, is a predefined function in WordPress, so you only need to call it. This function call is often included next to the function definition its mentioning. The following is an example of defining my_new_code and asks WordPress to hook it on:
   
   
   
   <?php

   function my_new_code($name) {

   echo “Hello ” . $name;

   }

   add_action(’the_location’, ‘my_new_code’);

   ?>
   
   
   
2. You can "add_action" all you like, but until you "do_action" nothing is going to change.
   
   say you had these functions in functions.php
   
   
   function function1() { echo "Hello "; }

   function function2() { echo "John!"; }
   
   You could simply add them to the init function
   
   
   add_action('init', 'function1');

   add_action('init', 'function2');
   
   And they will display at the top of your page without you specifically calling "do_action" because Wordpress is already going to "do" 'init' upon initialization.
   
   But if you add them to something that does not already exist...
   
   
   add_action("doit", "function1");

   add_action("doit", "function2");
   
   Nothing will happen until you "doit"
   
   
   do_action('doit');

Heres a list of all the existing actions you can "add_action" to

Link For Refe: Link

NOT: To say it briefly,

add_action/add_filter are for registering the action/filter to WordPress

do_action/do_filter are for applying that registered action/filter