I too did not understand how to install apps into the system until I found these instructions, you will need to root your phone first.Do you know how to set up the google play in system?
Any application I try to insert into the system is not installed.
If I try to insert an apk in system / app, it is not present in programs installed after the device restarts.
Thank you
I followed this article and managed to install Whatsapp into the system folder of this Rom on ver3.0
http://techbeasts.com/how-to-install-user-apps-as-system-apps-in-android/