How do I develop an Android application with a backend?

[AC Question]

how to develop an android application with backend

hello is there anyone who help me in this situation ..... i want to develop an android, ios and windows backend app and all of the above platform interconnected to each other in which i can delete, modify and insert the data and this effect all on the three platforms and from there i can manage my users and more options for ex: if a user make some changes in his profile in the app using android and later on if he surf that app in which if he opens his profile using windows app .. then it will effect thrice of android, windows and ios platform .... pleas guys help me out guys in this situation