couple days ago i was reading some of the threads and some said that if you want to talk to girls then just ask her anything ok so this girl who sits in front of me who is always laughing, talking and making fun of people, well teacher was teaching us something in math and i didn't really got it so i asked her
Me: Excuse me hmm can u plz explain me this problem i dont really get what
the teacher is trying to say
her: i don't know

she gives me a weird look and looks at her friend and they both laughs at me
then i look around to the other girl and ask her the same thing and she also does the same thing
this is what scares me the most i dont' know what to do when this happens can u guys give me some advice plz

I still get that sometimes from girls that remmeer me as an AFC. I'm not sure if it's denial or if they were just having fun or w/e. I'd say just let it go as it's 2 people in 6.5-7 billion. Mabye it's 8 billion now. idk.

It is most likely HOW you said it. Those girls probably thought that you were asking it in a somewhat AFC way. Remember to be confident when asking a question like that, and where did you read that what you stated was a good opener?
Personally, I would not take that road when making cold approaches with women.

She is in one of your classes, correct? Well, I am sure you see her around the school. One day, just approach her from there and ask a simple opener such as, "Hey, you are in one my classes, right?"
Make sure you are confident, you have a nice smile, and that you are able to be heard by her. Don't do this when she is not talking to somebody else, timing is VERY important as well.
You will find that once you meet her, you can start developing a conversation from there and than you can start developing deeper rapport as time goes on.

PM me if you would like some more info.