Child themes are the best way to customize your WordPress site because it allows you to update your theme without losing any customization.
To follow this tutorial, you must have a basic understanding of HTML / CSS and have a working knowledge of PHP and how it relates to WordPress.
To get started, you must create a new folder in your /wp-content/themes/ directory.
Next you need to upload a new style.css file with the appropriate header information which is linked above. The important thing is that you must specify template: parenttheme and import your parent theme's style.css file.
Once done, simply activate your new child theme and start customizing.
You can use Chrome's Inspect Element tool to identify specific elements that you want to change and add changes in your style.css file.
Next, you can also add a new functions.php file to add custom functionality to your theme.