I have a couple questions about several programming langauges(mainly languages for web pages[ex. html])?

What you want to learn is Java Script, it's a language you use to embed code in HTML pages and allows you to modify the page dynamically according to user actions and more. There are a ton of free tutorials in the web, if you know HTML, it should be easy. For mods i think you must learn a lower language, like C for example.