What I should learn to create a secure android or java app that connects to the server?

Question

(Please explain clearly)

Answer 1

Well as i used often PHP is very secure to connect with server and it's very popular or you can use Firebase and create host and databases on it.

Answer 2

Abdelrahman Ashref
Tnx and how can I be sure?
Do I need to learn its frameworks, libraries or any other stuff ?