Check the bottom left of the web/steam interface right above the "modules" section. It should say "BRANCH: $branch_name" the current name is the one the world you're watching is using and if you click on the name it will give you a list of other branches to choose from.

I haven't got around to watching them yet, but thPion has started a series of video tutorials over on youtube that might be of use.

Change "branch: default" in your gruntfile to "branch: BRANCH_YOURE_USING_IN_THE_SIMULATOR"

If you don't want to have to change your gruntfiile every time you want to push to a different branch you can use grunt.config to set it with command line arguments.

Did you play through the tutorial? Is it the game in particular you're having trouble with or JavaScript/programming in general? If it's the later the CodeAcadamy JavaScript tutorial recommended by the game's tutorial might be a good place to start. 

API documentation is intended for reference rather than step by step learning so I can see why it'd seem a bit obtuse if you weren't used to reading them, but you'll appreciate the organization later.