Finally someone brought it up.

In short, HTML and its partner CSS are used for Web Development.
However, they aren't programming languages just to be clear here.

This doesn't mean that learning HTML and CSS isn't beneficial.
To give you an example, my game was built using both (along with JavaScript). (If you want to see how that looks like so far, you can check it out here: http://www.graalians.com/forums/showthread.php?t=27245). That should give you an idea of the kind of things you can build with web languages,
but keep in mind that you're going to need another language like JavaScript, PHP or Ruby (even a combination of them) to actually make a game.

Getting back on topic here as mentioned above, Codeacademy is probably the best place to start if you want to go the web way, you can also buy books but Codeacademy provides a kind of hands on learning environment, so it's kind of like the learn-while-you-code rather then learn-first-then-code approach.
You can learn HTML & CSS, JavaScript, JQuery (which is just a JavaScript library), Python, PHP, Ruby, and not to mention that they've got a whole section on APIs (which I use for my game too) and projects that you can work on to strengthen your coding abilities.

That being said, and this is an important point to consider, most people wouldn't advise client side scripting (using web languages) to build your game, as there are server side languages such as Java, C++, C# that allow you to build the same games more efficiently and that will probably take you less time to code. I'm not an expert when it comes to server side languages, but if you don't care much about the web and you just want to make games, then that's probably the way to go. I'm sure many people here on Graalians can help guide you in that direction if that's the choice you make. Also if you're looking to build 3D games someday, forget about HTML and CSS!

Also, I'm learning Java at my HS at the moment, it's not to be confused with JavaScript. They are two totally different languages and the main difference is that one is client side (JavaScript) and the other is server side (Java). I think the name similarity was just a marketing ploy used back then to get people to start using the new language. Minecraft is an example of a game built with Java just in case you didn't know, and I believe that the Graal Client now runs on C++ (+Torque for cross platform compatibility).