I am confused about GCM Sender ID and API key. I\'m responsible for building 3rd party server that will send notifications to Android app.
Which one do I have to store o
It depends on how your thirds party server is going to work, but in general it works like this:
Information on how the developers get this information can be found in the GCM documentation: http://developer.android.com/google/gcm/gs.html
Depending on your needs there are third party commercial sever solutions available.