Change password function within Application

Hi,I am very new to APEX so i am still trying to get to grasps with the concepts of it so please bare with me if i use the incorrect terminology or am asking something silly.

I have been assigned to assist with various different areas within a project, one of them being to set up a function that will allow you to change your password on an APEX APP through the use of a change password button and through a first time log in feature, please note we currently don't have an email client/server.

The basic application has already been built so it is just a case of adding to it, however I am unsure of how to do so I have looked at various API's but am unsure with how to implement them, is there any way that one of you would be able to assist me/point me in the correct direction please to what i should be doing or where i should be looking as to finding out this information?