The main reason to create a child theme is so that your edits do not get overwritten when doing any sort of updates to your main (parent) theme. The steps are fairly simple.

• Source: https://codex.wordpress.org/Child_Themes

This example is for the Twenty Sixteen theme.

Navigate into your themes folder.

cd /<your_website_root_folder>/wp-content/themes/

Create a child directory within your themes folder and cd into it.

mkdir twentysixteen-child; cd twentysixteen-child

Create two files, style.css and functions.php.

Create style.css

Note: Update the appropriate fields.

/*
 Theme Name: Twenty Sixteen Child
 Theme URI: http://itsmetommy.com/twentysixteen-child
 Description: Twenty Sixteen Child Theme
 Author: Tommy Elmesewdy
 Author URI: http://itsmetommy.com
 Template: twentysixteen
 Version: 1.0.0
 License: GNU General Public License v2 or later
 License URI: http://www.gnu.org/licenses/gpl-2.0.html
 Tags: light, dark, two-columns, right-sidebar, responsive-layout, accessibility-ready
 Text Domain: twentysixteen-child
*/

/* Your code goes below this line */

Create functions.php

<?php
add_action( 'wp_enqueue_scripts', 'theme_enqueue_styles' );
function theme_enqueue_styles() {
    wp_enqueue_style( 'parent-style', get_template_directory_uri() . '/style.css' );

}
?>

Now go to your WordPress Dashboard > Appearance > Themes. You will notice that you now have a new theme called Twenty Sixteen Child.

WARNING: I ended up having to redo my Colors and Widgets once I activated the new child theme

Click Activate.