They are not similar. It is generally advised to work your way through the layers in a logical order:

HTML >> CSS >> Javascript >> PHP >> SQL >> Linux

It is suggested you understand those other technologies because PHP is predominantly a web language, and so you'll very likely encounter the above frequently. This is a *massive* journey. I'm not sure what you're end goal is, whether to be competent enough to tweak websites, or if you plan to make a career out of it, but there is a mountain of information to cover.

There is a clear divide between the above technologies, this is split into Frontend Engineer (Design, HTML, CSS, Javascript), and Backend Engineer (PHP, SQL, Linux). If you want to be a full-stack web developer, then climb from frontend to backend.

Try Learn to code | Codecademy if you want to dive in.

To be honest, trying to progress from HTML and CSS to PHP or even JavaScript can be very difficult and tedious if you don't have prior programming experience. This is because, lessons learned from HTML and CSS have little to nothing in common with PHP and JavaScript, logically speaking. In practice of course, these things are used together often, in web projects, but the logic it takes to say, mark up an HTML document, won't help you understand, say, the order to loop through data sets when generating HTML tables with PHP.

For sure, you need to understand HTML and CSS before learning JavaScript or PHP, which is why it is so difficult for some people to learn either. In my opinion, it is better to learn another, general purpose programming language, before attempting either. You don't have to become an expert in whatever you learn first, just learn the basics, get good enough so that you have memorized core fundamentals. You'll find this will help you comprehend the generally more complex task of mixing style, markup (CSS, HTML) with logical languages.

Why don't you try learning the basics of C first? PHP is based around its syntax, and so are a slew of other languages. Most programming languages are, in fact, "C Family" languages.

Thank you everyone.

You have definitely cleared some confusion.

I have already learnt some basics of JavaScript in w3schools.com and I found it very interesting. I think I will start there, then move onto the more advanced languages.

Thanks again
Daniel Carton.

Well, it's easier to move from a statically typed language to a dynamic one than it is to do the reverse, so it's always a good idea to have 1 or 2 static languages under your belt. C is even more difficult than other static languages in fact, since you have to do your own memory management if you are going to do anything dynamic with sets of data. If you can learn to do this, something as relatively easy as PHP will be a breeze.

But my point was really, general programming, without the complication of learning web development at the same time, will make the ultimate learning of doing dynamic web development much easier. My first languages were BASIC and Pascal, and this was hugely helpful later in life.

HTML 5 >> CSS 3 >> Javascript >> PHP >> SQL

this is the manner you can proceed

In my opinion, you should learn JavaScript first. Because PHP files can contain text, HTML, JavaScript code, and PHP code. So you must have the knowledge of HTML and JavaScript. It will help you!

I started my knowledge of php, by hacking free php scripts for my own sites and doing installs here on the forum.

By hacking, I mean modifying to better suite my site, or adding custom things.
After enough of that I decided to learn more about it, and most of my knowledge came from PHP Tutorial - Introduction

Now I consider myself a pretty good programmer. Best of both worlds, I understand the need, the marketing, and the coding

Learn HTML,CSS and PHP. JS is too hard, let it later.

I can't stop laughing.