I'm creating a personal project, an Android application, where user sign ins via a server are essentially. Also users will be able to share important "updates" in both a data stream that all users can have access to, and potentially down the line a data stream that will be specific to local users.

Unfortunately I have basically no idea of how to implement the server for this application. I'm confident that I'll be able to create a solution though, I just need to be pointed in the right direction. Are there any existing servers/api's that I could access that will allow me to handle my "connected" tasks? If I were to make a server myself for this application where should I start?