How to develop a social network mobile application from scratch?

Question

Android

Good day.
I warn you in advance, I'm a complete newbie with a big mess in my head.
More to the point, the idea is to create a mobile application with a wall of text posts and the ability to open chats.
My approach:
1) create a backend in a spring boot with maven, hibernate, etc.
2) *to the server?*
3) solve all problems using flutter.
However, no matter how much I google, I can’t find exactly how I can go from the first point to the second. Perhaps everything is wrong, but in this case, I can not find where to start.
Do I need to choose something like firebase or create my own server and upload the code there (Advice on how to do this is very welcome)
In the future, this idea is planned to be developed both on IOS and on the Web, but as you can see, there is a catch in using the back.
Articles, book titles, videos and any materials in general are very welcome.
Thank you in advance.

Answer 1

Usually they start with an idea. After formalizing the idea in the TOR, they choose the tools, then calculate how much it will cost, then they go to the investor for money.

Answer 2

This is how a product is created (with minor differences based on the authors):
1. An idea appears
2. It is thought over, different implementation options are looked for, pitfalls are looked for, details are considered, how and what will work and interact with each other - briefly: brainstorming
3. At the computer still no one sits down, they take a pencil or pen and write architecture on paper, they think over how and what will work in detail, what classes will exist, what methods they will have, how it can all be divided into logical parts. Usually this is done by a person with a corresponding position.
4. Technical specifications are drawn up for programmers, because programmers write code, of course, a good programmer must also be able to build architecture, but when you have a team, this is difficult to implement.
5. Programmers begin to write code according to the TK, everything is clear for them and having a normal TK is very easy to work with.
In this list, I missed various marketers, psychologists, analysts, designers, etc. there. etc.
But I think the essence is clear, just like that an idea came up and you can’t start writing code right away. For then you will rewrite your own code dozens of times trying to make changes.

Answer 3

Try to do something simpler, at least a chat to start

Answer 4

I once did a similar thing, I had a server on flask (python) you can host either on Azure or on Heroku (well, there are a lot of other platforms, but I haven’t tried them). The database was Mysql communicated with the server via sqlalchemy. And then, on requests from flutter, the application received data from the server. (but that's all in a nutshell)