In WordPress, a child theme is the counterpart to a parent theme. Creating themes is only for developers, so if you’re only interested in administering a WordPress website, then you won’t have to worry about parent or child themes.
When WordPress was first developed, there was no way to change or modify the theme. Then, after the ability to change themes was included, developers began wanting to make their own themes. WordPress made this easier to do by allowing child themes, which are copies of a parent theme that can then be modified.
For example, if you’re using a theme that you really like, but you want to make some changes, you can create a child theme. The child theme will inherit all the scripts, functionality, style, and abilities of the parent theme. The only difference will be the modifications that you make to the child theme.
The benefit of having a child theme is that any updates or modifications to the parent theme are immediately preserved in the child theme as well. For example, if a script in the parent theme is updated to patch a security hole, then the child theme, too, will automatically use the updated script.
To create a child theme, you must make a new folder in your themes directory. The first file in this new directory must be your CSS file (“style.css”). It’s usually a good idea to add a comment in this file noting the parent theme. You can then begin adding any customized files that you like for use in your child theme.
To see the child theme in action, it must be activated as your WordPress site’s theme. Any file or functionality not included in the child theme or overwritten by it will be taken from the parent theme.