Told you it was a stupid question! I was sitting staring at that page
However, I can't get it to connect. I am putting my information into Calibre in the format you proscribe ie
http://username(colon)password@computer:8080 (sorry the : sign on my computer is inserting an emoticon in that address)
Calibre says that a password is incompatible with some devices - maybe that applies to the ipad. I also have a little android tablet where I am running Aldiko. That asks for a username and password rather than incorporate it in the url, and is letting me in.
I guess I need another think tomorrow, after a good night's sleep.