How to use phpBB as a data model to learn and master php

[MGadAllah]

what is the thing I need to keep in mind all the time to make code secured as possible?

Validating user input and the number one rule for that is test for what is expected. e.g. If you expect an integer you don't test for exploits, you test to see if it's an integer.

There is lot of forums around people will offer you advice on programming, post your code and ask them what if anything is wrong with it.

Thanks a lot and much appreciated your advise that I will follow to the letter
Please accept my apologies for the late reply.