i found http://visualjquery.com/ more useful when i was learning jQuery with each function explained in demo along with code sample in a practical manner.
im looking for the same in mootools. is anyone find any website which provide demos and sample coding like above the same in visualjquery.com
As Nick and Tim mentioned, the best resource is the documentation, but to make stuff more interactive, you can play around with the code within jsFiddle's context - example: http://jsfiddle.net/oskar/c6n7q/