I want to know the idea of chat programs Screens such as WhatsApp, Messenger, Telegram, etc
1- There is a scrolling screen with a dynamic list of friends, and an unlimited number of friends can be added +
2- You can click on any friend, enter his chat screen, go back to the list screen, and so on
How can such programs be created, what extensions are used, and are there AIA examples?
A basic example
https://appinventor.mit.edu/explore/ai2/clouddb-chat
Modify the example to most of what you hope to achieve.
Search the community for 'chat' for more examples. 
Herre is another example