All websites use a combination of languages depending on your needs
Basics:
HTML - this is the structure of every website. An absolute must, can't make anything without it.
CSS - Used to add styling to your code. If your HTML is the frame of your house, CSS would be the paint and decorations.
Function:
Javascript - this is used to add neat functionality to websites. Animations, moveable elements, pop up windows, AJAX content loading (update a section without updating the whole page) etc. It ties into and manipulates the HTML and CSS of your site. Javascript functions are often directly initiated by user interaction and is known as a client-side language.
Advanced Function:
PHP / Ruby / many others - are server-side languages, which means your user never actually interacts with them, they only see the result. Not necessary for a basic website, but they can definitely help if it's something that is meant to be updated with any regularity. Many times these languages will also interact with databases to store information.
I suggest getting started here:
http://www.codecademy.com/tracks/web and let me know if you need any pointers.