enqueue-scripts-child-theme.php

add_action( 'wp_enqueue_scripts', 'my_custom_script_load' );
function my_custom_script_load(){
  wp_enqueue_script( 'my-custom-script', get_stylesheet_directory_uri() . '/custom-scripts', array( 'jquery' ) );
}

enqueue-scripts-plugin.php

add_action( 'wp_enqueue_scripts', 'my_custom_script_load' );
function my_custom_script_load(){
  wp_enqueue_script( 'my-custom-script', plugin_dir_url( __FILE__ ) . '/custom-scripts', array( 'jquery' ) );
}

footer-script.php

<?php
/**
Plugin Name: Footer Scripts
*/
add_action( 'wp_footer', 'my_footer_scripts' );
function my_footer_scripts(){
  ?>
  <script>alert( 'Hi Roy' ); </script>
  <?php
}

header-script.php

<?php
/**
Plugin Name: Header Scripts
*/
add_action( 'wp_head', 'my_header_scripts' );
function my_header_scripts(){
  ?>
  <script>alert( 'Hi Roy' ); </script>
  <?php
}