What should we talk about when we meet our girlfriend's parents? I don't think I have anything to say! I usually talk less, and my girlfriend can only talk a few words every day.

You can ask her parents about their health, what kind of sports and exercise they usually take part in, and also introduce them to your parents, hobbies and interests. You can also ask them about some of your girlfriend's childhood stories, and when you come across a topic they are interested in, you can talk about it down the line.