Don't worry. I was nervous too. Extremely nervous. But there's nothing to be scared of. Martial arts teachers seem intimidating at first, but they're actually really nice people once you get to know them. Take my TKD instructor for example. He knows how to throw people, how to knock people out using pressure points, how to do crazy spinning kicks. But he’s literally the kindest person I know.
As far as weapons, it really depends on the style. If you're doing taekwondo, you might use weapons, but it's not a huge part of taekwondo. Taekwondo focuses on kicking.
Whatever style it is, you probably won't get hurt. My instructor said he's gotten more injuries from soccer than he has from taekwondo. Injuries do happen - but if you listen to what your teacher says, you'll be okay.
And don't worry about everyone making fun of you. Chances are, if anyone makes fun of you, they will be younger kids, who can easily be ignored. Show them who's boss. Don't listen to what they say about you.
Some people at school, when I was a gold belt (yellow belt), made fun of me, but I always told them, "I may not be a black belt, but I can still kick your (rear end)."
Hold your head high and believe in yourself. You're not going to be great when you start - I sure wasn't, and I'm still not perfect - but even Bruce Lee had to start at no-belt. Even when you get to black belt, you will still make mistakes. Everyone does. But don't let that stop you.
Keep calm, stay focused, and do your best every class! :)
Make sure you yell when you kick, punch, etc. Yelling is going to be weird at first, but yelling when you're a beginner will pay off later.