I take small doses sometimes when I feel like I might melt down in public or at work. It's a basic tranquilizer. It makes you feel calm. Things don't bother you as much. Sort of numbs you and your senses a bit, so you don't freak out about anything. It also can make you very sleepy, and give you "dead" looking eyes, especially if you take more than you need. If you've never taken it before, you will have no tolerance for it. Depending on how well you tolerate drugs, it might affect you more strongly than you expect and you could even fall asleep. It will definitely not make you talk more. You'll probably be quieter than usual and sort of distant.
My advice if you expect the wedding to be overwhelming is that you take it with you, in your pocket or wherever. If you start to feel like you're not going to make it, break the pill in half and take that. You will start to feel it in about half an hour. You will know when it has started to work. If, after fifteen minutes or so of it working, you still feel like you need more, take the other half.
Do NOT mix it with alcohol. I once had half a Valium and two beers, and I completely blacked out. No memory whatsoever of what happened after that. So if you're considering taking it at the wedding, plan to not drink. I have a lower tolerance to chemicals than most people, but I don't think it's worth the risk.
I don't have any further advice on weddings, sorry, but I figure you should have the information about this drug before you take it.

Thanks! I just broke a valium in half and tried it.. right now I'm feeling okay. I don't know yet.. I'll see later how things are.