how to edit child theme? *Responsive Theme

So, I been wanting to ask this for quite some time – I’m very new to WordPress so bear with me.

I’m currently using Responsive Theme – its Child Theme, where it contains just 2 files, style.css and rtl.css

Always wonder whne I see some guys advising on editing some .php files in Child Theme other than both mentioned files, I can’t help but wonder how do I go about editing those other .php files which I don’t eee in the Child Theme?

And if you guys have any good source for reading – in relation to this question of mine – I often see people advising on pasting or editing some codes without referencing to which .php file is involved. I’m sure there’s a guide somewhere to tell which file to edit when it comes to certain things – but I’ve yet to find them (a guide).

Thanks for reading this rather lengthy questions!