Answer 1

Sql is used to manage database, before this you need to learn some backand language, after you can make some powerfull apps.

Every complex app or website need database to store user data.
For websites simplest learning path is:
Html, CSS, JavaScript (frontend - things user see on its device)

Php or java or python or any other backand language what can be used for websites + sql (backend - managing user data and storing it on database)

If you learn all of this you can make any website by yourself with enought practice.

Answer 2

PostgreSQL, MySQL... 😁

Answer 3

PreSQL before
PostSQL after