Learn Javascript

i want to write a code using java script.i m creating asp.net web application and language is VB.I m totally new to .net could you please guide me how to start and from where to start?So that i can use java script for browsing folder on server and language of my project is vb.Guide me so that i can learn basics what is java script, why to use ,where to use and how to use....all your previous solutions are really helpfull.