title: How to send FCM push notification message from app server to mobile clients?
body: <p>I have already developed a simple application for both iOS and android. Now i want to implement push notification services for both apps. So I would like to implement FCM(Firebase cloud messaging.) service for sending push notifications.I read the google docs but have some doubts. My app server have all my users data. I want to send notification to single, multiple and all users from my app server based on needs.
  FCM Tokens are needed to send push notifications from app server to mobile clients? What are the things to do in both mobile and server side? Can't find clear ideas.</p>
  
  <p>FCM is only for intermediate to send push notification message? 
  Do we need to store any user details in Firebase? Because all of my users data in app server. </p>