How to start developing an Android application for an existing PHP online store and front-end developer?

Question

PHP

From what instrument...
Any parting words are important. Thank you all in advance for your replies.

Answer 1

I guess you should pay attention to ionicframework.com/getting-started or https://facebook.github.io/react-native/ if you have a frontend developer.
Writing a native application is quite a long process, especially if the stack is unfamiliar.

Answer 2

You should start with the official documentation https://developer.android.com/