The only thing you need to build a website is html or xhtml. You don't need any of the others, but they all add a lot and help make a site better.
Learn html or xhtml first. In fact learn xhtml. From where you sit both are really the same, but xhtml will help make you a better coder. Either will take the same amount of time to learn. Think of xhtml as a stricter version of html that forces you to write better code.
Next learn css. xhtml will be how you structure your pages and css will be for presenting those pages. For example xhtml will have you put your content inside paragraph tags <p></p>. CSS will tell the browser to make the text inside that paragraph green or show it as a certain size of display it in a specific font.
JavaScript is for programming things on the front end. The front end is the browser. In general when you see cool effects like items fading in or out or sliding across the web page it's being done with JavaScript. It doesn't have to be, but it's the likely culprit.
PHP is for programming on the backend. Any server side language like php becomes much more useful when you combine it with a database. PHP is usually associated with MySQL, but there are other language/database combinations.
A lot of backend programming comes down to having a database to store your information and having the server side language read and write to the database.
You won't be able to learn all of the above at once. In fact once you get into all of the above you'll never stop learning them. Things change and there's always new things to learn.
The order I listed above is probably a good way to approach learning them. xhtml is relatively simple to learn. You could reasonably pick it all up in a week. CSS isn't much more difficult to learn the basics, but it can take some experience to use it well, particularly when it comes to site layout. Again not really hard to understand.
JavaScript has one advantage over learning PHP in that you don't need to install PHP on your computer to get it working. Just type away since the magic happens in the browser. It's not necessarily an easier language to work with than PHP, but it'll probably be easier to get started with it.
Hope that helps. Just take each one at a time and start learning.
