can someone provide me with a sample of how to branch on a variable? I'm trying to set up a log in screen which will go to a particular url if the correct input (variable) is entered into a text box. Seems simple enough!

On Nick's site you find some examples, one of them includes this.
http://www.friendsofcourselab.info/

That's a simple and kind of artificial way to branch. It does have drawbacks.
What you really need is what is called SCORM simple sequencing.
The only problem being that while it's called simple it is anything but. Courselab does have this, see the controller component, it is also very complex and quite poorly documented.