You can see the source of any page by putting "/.edit" before the first slash in the URL path. For example the file you are reading can be edited here:
Anybody with an account can edit files, and anybody can get an account. It is free.
Sign into this site using your Google account. (Details: when you sign in, this site will know your email address, but we will not share it with anybody. Your password is kept by Google, not by this site. If you use a gmail address, it will be the same password as gmail.)
(You can also just establish a password on js.dabbler.com. Be aware that local password support is not yet full-featured - once you pick a password, you can't change it, etc.)
When you sign in for the first time, you will pick a dabbler username that other people can see, and you will get a directory "/home/yourusername/" where you can put files that only you can edit. Anybody is free to edit files in the /public/ directory.
The /examples/ directory is full of examples you can try, copy, and change.
The instructors are David Bau, James Synge, Joon Lee, Thomas Colthurst, and Anthony Bau. David, James, and Anthony put together the site based on previous similar efforts by David and Anthony.