Child theme different concept in "Wordpress".
Child theme is the inherited properties theme.Means:-It inherite the properties of basic theme or default theme.
Basic Files needed:
basic file needed in child theme is style.css.
Facts:
If you create a new function.php in child theme then parent theme function.php get combined with child theme's function.php.So if you need new functions in child theme the create function.php with new functions.
Needed:
In style.css you need to write at top something as-
/**Theme Name:Themename*Theme URI: Themename's-homepage*Description: brief-description*Author: your-name*Author URI: your-URI*Template: use-this-to-define-a-parent-theme--optional*Version: a-number--optional*/