I would look at: http://www.letscodejavascript.com/

The first few episodes will help you get setup with an actual development environment and set of tools so you can code on your own machine (as opposed to the magic "just type things into this web browser"). The series is also a very good introduction to testing and TDD.

If that is too overwhelming, try some of the Code School Javascript courses - they are similar in that you will be typing code into the browser but they should have some new material.