SQL is the language most commonly used to provide stored content on Web pages.  You have probably been given SQL data many times as a user.  Anything you bought online was probably listed from a database and your order was stored on the database.  Any Web-based communication probably happened through a database.  Social networking, search and most large sites all use databases.  This site has almost no pages as they are created from database data when needed.

You can already create pages which change slightly through the use of PHP.  Adding SQL means pages can change every time they are viewed and can be updated by users for other users.  Pretty much any site which you can think of either uses a database or would be better if it did.  Unfortunately databases are also hard to get right but worry about that later.

It is probably worth accessing your server and creating a new sub-folder for your work on SQL.