edit a functions.php via childtheme

Hi there,

I have created a childtheme (to be on the safe side, in case of theme updates :)

now I try to edit the funcionts.php.
If I copy the functions.php from your theme (parenttheme) to my child theme directory, I receive an error :(
With all other php files it work´s like this (fe. with the header.php).

In google I found out, that I have to do changes in functions.php in childtheme in another way?!
Can you explain me how that works?
Which file I have to upload in my childtheme – directory? And do I have to change somethin in the functions.php in the parent directory too?

in the functions.php at the parent theme I saw:
/*
* if you run a child theme and dont want to load the default functions.php file
* set the global var below in you childthemes function.php to true:
*
* example: global $avia_config; $avia_config[‘use_child_theme_functions_only’] = true;
* The default functions.php file will then no longer be loaded. You need to make sure then
* to include framework and functions that you want to use by yourself.
*
* This is only recommended for advanced users
*/

What I have to change in the bold passage? I´m not really sure, what to do with that information…

Thank you very much,
Greetings Miriam