facebook and databases

Hello, so new to the forum and new to the development of back-end and sql. Currently studying the course of foundations ciw. I have a particular project in which I intend to start working and at this moment I am only investigating. The site I have in mind is similar to Facebook (only on a much smaller scale), so my question is, how is the Facebook database structured?

What happens when a user registers for the first time? Has a MySQL database been created specifically for that person with several tables for user information, account settings, statuses and photos?
SEMrush

I'm mostly curious about how the Facebook status feed works. I imagine that when someone publishes a state, the state is sent to a cgi script that takes the status of the users of the publication and registers it using sql in a table in the personal database of each friend. In my limited experience it makes sense, right? But I imagine that data replication could be a problem. Is there a better and more efficient way to make this work?

Thanks in advance