How to create a child theme in wordpress ?

first, you need to create a folder in wp-content/themes/YourChildthemeName Suppose we are creating a child theme for the twentyFifteen theme. then we can put our child theme name to twenty fifteen-child The most important thing about child theme is consist of two files that are functions.php and style.css. These both files are just a copy of the parent theme. The style.css consists of below code just copy and paste:
 Theme Name:   Twenty Fifteen Child
 Theme URI:
 Description:  Twenty Fifteen Child Theme
 Author:       Developer gang
 Author URI:
 Template:     twentyfifteen
 Version:      1.0.0
 License:      GNU General Public License v2 or later
 License URI:
 Tags:         light, dark, two-columns, right-sidebar, responsive-layout, accessibility-ready
 Text Domain:  twentyFifteen-child

functions.php You can make this file blank. that's it..