A doubt with child themes

Hi!

I’ve been reading about child themes and the reasons for using them, but I wasn’t able to find an answer for my question.

If I’m getting it right, when I want to edit a theme’s file, I have to copy the original (from parent’s theme) to the same location on the child’s folder and then make modifications on it and when wordpress generates the website for the visitor, the file that will be used is that one.

But what happen when the parent is updated? How are the changes made on the parente by the developer reflected on the child? In the map of my mind, those changes are never reflected on the child, but I am missing something, right?

Thanks in advance for your patience.