This is the question my grandad asked, a couple of months before my partner's and my civil partnership ceremony - which is due to take place next week.
Bearing in mind he suffers from dementia, and has been told about the day a few times, we patiently explained once again.
It's not that different, in our case, to a heterosexual civil ceremony. A registrar will take us through a legal ceremony and contract. There'll be music, dancing, food and drinking. Plus two women in dresses and no groom. That's the only difference in the way we've chosen to celebrate really.
Luckily, once explained, my Grandad 'get's it'. Every time we talk, he asks how the plans are going.
That's not been the case for everyone. We've had a really mixed response from the various suppliers to the wedding. A lot of acceptance, yes, but also a lot of ignorance, denial and outright rudeness. One suit salesman kept asking about the groom, for example, and the groom's suit despite being explained to that there were 2 brides and no groom. Or the flowers and decorations supplier who could not understand why we'd want to pay for two bridal bouquets.
We've had 3 years to plan and to make sure that what happens at our gay wedding (sadly I can't officially call it a marriage yet) is our perfect day and a chance to celebrate with our closest family and friends our lifelong committment to one another. Let's hope that's what happens at our gay wedding.