A child theme consists of at least one directory (the child theme directory) and two files (style.css and functions.php), which you will need to create (WordPress Codex: Child Themes)
1. Create new directory in wp-content/themes
Name is completely optional. Example:
2. Create stylesheet file
File name style.css is required.
Theme name can be whatever you wish.
Template must be directory name of parent theme, in this case sircon-express
Theme name: Express 2 child
The lines above gets the job done if you wanna create things quick and easy. WordPress now understands that the theme “Express 2 child” is a child theme of the theme found in “sircon-express” directory.
You can also add additional theme information in the stylesheet header (example reference: WordPress Codex: Child Themes )
Theme Name: Twenty Fifteen Child
Theme URI: http://example.com/twenty-fifteen-child/
Description: Twenty Fifteen Child Theme
Author: John Doe
Author URI: http://example.com
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: twenty-fifteen-child
3. Create functions file
File name functions.php is required
… Fill it with whatever you may please!
Your child theme is now created. Time to start overriding, adding cool features and style your child theme