To understand how BootstrapBase themes work you need to look at how Bootstrap 2.3.2 works first.
You can download Bootstrap files from here... https://github.com/twbs/bootstrap/archive/v2.3.2.zip
When you have unzipped the file you will find the Example files in the docs directory. These files contain the HTML code of various ways to make a page look and work differently.
Hope this helps:
Mary