Thanks to the JHB meet-up people for pushing me on the git issue.
I gave up the weekend and with advice from Nick to refer to the open source git book http://git-scm.com/book sat down and got to work on learning git.
I'm only on mid-chapter 2, but also read a bit of chapter 3 and already managed to get some stuff done:
On Drupal.org I managed to set up a sandbox and put a theme, Zen Slate, in there: https://drupal.org/sandbox/nightwatch/1981700
On github I also managed to set up Drupal Remix, an installation profile. It's remix.make file then uses git to get the theme from my Drupal.org sandbox so that that theme is the default after install.
If you have drush and git installed, follow the instructions on github to have a nice test site up with loads of module pre-configured:
https://github.com/RiaanBurger/drupal-remix
Thanks again guys - you opened a whole new world for me.