JavaScript is an object-oriented scripting language used primarily on the client side in the web browser to achieve dynamicity in the content. The name is arbitrary and regrettable: it has nothing whatsoever to do with the Java programming language.
JavaScript is C-like or Java-like in its syntax just as are C++ and C#.
A good book on JavaScript is Head First JavaScript.
MooTools is a popular JavaScript framework. It eliminates the need to invent a lot of common, useful infrastructure in your own JavaScript. It accomplishes this through libraries, downloadable as a simple JavaScript file (.js) that is unceremoniously loaded by your HTML documents.