As the manual link states, checkboxes only work in [plain lists](https://www.gnu.org/software/emacs/manual/html_node/org/Plain-lists.html#Plain-lists).  Your example uses [headlines](http://orgmode.org/manual/Headlines.html).  You need to use the checkboxes this way:

    * shopping list
    
      - eggs
      - bread
      - Tesla Model S
      - bacon

Now, when you're on "eggs", you can hit `C-u C-c C-c` (`C-u C-c C-x C-b` also works) to toggle the checkbox.  `C-c C-c` will then toggle whether the checkbox is checked or not.

If you are already in a checkbox list, then `M-S-RET` will add a new item with a checkbox.