How to properly use app/config.xml vs plaftorm/.../xml/config.xml

Hi, I’ve been working with Ionic and ngCordova for a while and I have come to a question…

I can’t understand how should I use the config.xml file that is in the root of the project, when should I use it, and when should I use the config.xml files that are inside each platform files.

I have read the Cordova documentation here that talks about config.xml file but I only got more confused about it.

For example:
When I want to use a cordova plugin such as org.apache.cordova.geolocation, since I register it to my ionic project via corodva plugin I dont know if I have to add the <feature></feature> tags inside the androids config.xml file or the registration itself does this for me. I understand that I must add some permissions to the android manifest but I’m not sure if I have to edit the config.xml file, or to edit the app/config.xml

Can anyone explain me how this works?

Thank you very much!