I am always going to my friend's house (who is a really big Lord of the Rings fan) and play Dungeons and Dragons (a role-playing game about medieval times)
My friend says nerds play it, but I know nerds are supposed to be smart. But I don't really have awesome grades in math and stuff. Am I a nerd, or just a dork?

Oh please, you are whatever you feel you are, not what some 'friend' decrees far and wide across the land.
I'll bet you are plenty smart if you play D & D. There are many kinds of smarts.
I come from a time when nerds were automatically assumed to be dorks. It took nerd appreciators like me to change attitudes. I was an appreciator before it was fashionable.
Don't worry what people say. I know that sounds trite but it's true!

LOL... this is funny.

I'm a dork. Why? Because I like Batman. I like Science Fiction. I used to play Dungeons and Dragons. I have a small collection of tarantulas and can name them using their scientific names. I do all these "silly" things. Although I am fairly intelligent, I don't consider myself to be smart enough to fall into the nerd category so therefore I am just a dork.

Now two things about this that I want to tell you...
1) Don't let this label affect you. If someone calls you this, so what? It really doesn't matter. You are who you are and don't let a silly label like this affect you in a negative way.
2) I have found that there are many girls/women that actually like dorks. Now that is a positive way to look at it.

Epppp Odinn I am a dork/nerd as I am a gamer and a female at that. But I draw the line at spiders. So yes some girls love being with someone with the same interests as them. I am married to a dork/nerd as well and have been with him since 1991.
I am thinking you are fairly intelligent as D&D takes some smarts to remember how to build an effective character (getting your feats, putting your points in the right slots, buying gear to maximize your character). Also remembering your powers and how to use them effectively in battle.

http://www.bitrebels.com/wp-content/uploads/2011/02/Hello-My-Name-Is-Geek.jpg ;)