Well, I learned the most about computers on my own, after taking a BASIC class in the 10th grade. I did eventually get a BS degree going to school at night, after about 13 years. By then I had been programming professionally for about a decade.
So, you've learned some about HTML. It describes how a web page is structured. There's some formatting that can be done with HTML, but the standards committees are trying to remove that. They would like everyone to use CSS to describe things like bold, italic, fonts, sizes and colors. Both of those languages are static and descriptive; they have very little to say about making web pages dynamic. To do that, you add JavaScript, which runs in the user's browser and can create and delete HTML and change CSS information. All of this is downloaded from the websever. Often these are just text files on the webserver, but if they are customized for each user, then probably a program written in PHP creates or embellishes the HTML. If the information needs to come from a SQL database, PHP provides a way to pass SQL statements to the database and get results back.
To get started with just HTML, you can use Notepad or any simple text editor to create a web page on your local machine. After saving it, you can double click on it and view it in your browser. In this way, with a book on HTML, you can teach yourself to write HTML and test it on your own PC. You can do the same with CSS and JavaScript.
(There are much better, free editors than Notepad, but you don't have to have anything more than a browser to start learning web programming.)
