How to make a “child theme” for WordPress. A pictorial introduction for beginners: Demetris has put together a comprehensive, step by step pictorial instruction set for creating your own Child Themes for WordPress. He assures me that the set of instructions are easy to follow. Child themes are WordPress themes that behave like parent themes (or a main theme on which the child is based) and inherits all the characteristics of parent themes including options pages.
If you like a theme, want to make small changes to the way it looks but do not want to make changes to the core theme files (for future updates etc.), child themes are the way to go. Remember to send Demetris a thank you if you like the work he has put into this documentation.