HI Jem, I have just got my Avatar up and running and I think I had the same problems you are having by not seeing the box they all talk about.
When you have done all the business with Gravatar, Return to this site, click MY PROFILE, then click EDIT MY DETAILS.
The first line on the next page says "Your Avatar is inactive", Highlight that wording and a small box with a dotted edge appears underneath at the beginning of the next line. Double click on that small box. (I think your cursor will change to an arrow when you are over the box).
Now go to the bottom of the page and there is a button with SUBMIT written on it.
Click on that button and hold the mouse button down for quite a while as I don't think this submit button works straight away.
Eventually the page may move to the top and your Avatar should be showing.
That is how I finally got things to work for me.
Good luck with it, Jem