All the elements on a website is more or less inanimate unless if you spice it up with some Javascript or Flash. Flash is pretty old news now so we wouldn't suggest using it unless if there is such a special need for it.
Javascript is also a kind of programming language that alters a website when it is loaded. For instance, if you want your page to show a popup when a button is pressed on, Javascript can make that happen. If you want to replace the visual look of your scroll bar, Javascript will do that too.
Again, lucky for us, jQuery is a Javascript library that also has almost everything you will need pre-written for you, so all the special effects from popups, to mouse hover animation, etc. you may need for your website are readily available for you to plug-in and start using. jQuery is so popular that almost every website you visit uses jQuery.
See some great jQuery examples here
JavaScript
