Hi Helen, thank you for your testing. The more people test the better and more friendlier we can make the site before we go 'live'.
That field, the "HTML embed code", is irrelevant and confusing. I've looked at the gallery options and cannot find an option to get rid of it so I will see if I can manually change the page's code when I've next got time at home. The "Direct link" is also irrelevant and can go.
So in answer to your first question, the field you want is the BBC embed code - can you think of a better name? If you click the (?) you'll see it's got all sorts of options for the amateur geek
In answer to your second question, there is not yet an explanation page. I've asked for a volunteer (see
here) but no takers so far. Would you like to write one? There's many ways of adding a picture on here, so if you can write about one of the methods it will be a big help.