The quick and easy version is here.
The full version of the form (in which you don’t have to answer all of the questions anyway, and you can be certain that they won’t have a “came from the Christian Institute” link on their stats) is here, and the document itself (not as abominably written as that old education consultation one was!) is here.
You have until 11:59 pm tomorrow, but gonnae just do it now? You don’t have to be resident in Scotland, contrary to the message given out for the past x weeks (apparently – no idea if this is actually the case, but so I was told and am repeating it to make you feel the urgency a bit more! – the pro-gay-marriage side have been sending in submissions all this time from all over the place, so we’ve been rather wrong-footed and need to catch up).
Edited to add: Useful short article here, if you find it is taking you ages to organise your thoughts. The questions on the response form are of a “Have you stopped beating your wife?” kind. The principal argument against homosexual marriage applies to civil partnerships as they currently stand, though Lazarus’ third point (three handy points here, and some stuff by John Haldane) makes one that uses the fact of their existence to argue against introducing homosexual marriage.