It's been a long time since I was exposed to laughing gas (nitrous oxide), but I had a lot of dental surgery as a kid and that's what they used commonly back then.
It's just what the name says, they put the plastic mask over your mouth and nose, and you breathe it in, it has no smell or taste as I recall, but it can make you giggle and laugh like a crazy person, then the next thing you know, you're waking up in another room, like nothing happened, and it's all over. You may feel a little woozy for a while, and need someone to steady you when you walk to the car, but that's about it. Go home, go to bed, and read a book. You'll be fine.
_________________
"I don't mean to sound bitter, cynical or cruel - but I am, so that's how it comes out." - Bill Hicks