Gravatar Confusion

My forum ID is different from all my blog IDs.
I don’t know why – it just happened that way.

But I seem to ask so many questions on here, I thought I needed an avatar (maybe to help people run a mile when they see it lol!)

Anyway I signed up with Gravatar, and I have no idea what to do with the URL I’ve been given.

I don’t have a blog with this username (Rustybulb), so where do I put the URL?

Thanks