I know this has been asked before but I'm still scratching my head.
I need alter some PHP (I need to move the nav bar to underneath the header on TwentyTwelve).
I have created a child css file and edit this file frequently.
The question is: How do I add and PHP child theme? I have been searching for a long time but cannot find the answer.
Please can someone give me very simple step by step instructions on how to do this.