what is do_action in wordpress code example

Example 1: wordpress add action

// Hooks a function on to a specific action.
add_action( string $tag, callable $function_to_add, int $priority = 10, 
            int $accepted_args = 1 )

Example 2: wp add_action

add_action('wp_footer', function($arguments) use ($myvar) { 
    echo $myvar;
}, $priority_integer, $accepted_arguments_integer);