Fixed: in the JotForm settings, click the magnifying glass next to the “Form ID” field, then sign up for a free JotForm account. Then you can create your field, but the problem I now have is that you can’t seem to make small changes to a form you have set into your website; you have to go right back and create another, and I haven’t worked out how yet.
On the other hand, son after I had logged an account with JotForm, an email came from them saying welcome and all that, but it wasn’t just an automated response. There was actually a person there emailing back. That’s good service!!
So I’m emailing back for an answer to my questions above, will post back shortly (but forum rules say I should post it in a new post… will link to it soon).