Hold the brakes. You're not even in high school yet, and you're worried about how to become a neurosurgeon. There is
PLENTY (notice the emphasis) of time before you have to worry about becoming a doctor, let alone becoming a brain surgeon. Enjoy your time in high school; you only get it once. Just have a general idea of what you want to do (healthcare is a good focus), and decide on the specifics later. I know where you're coming from; I was the same way. But don't create such a narrow mindset where you'll ignore other career areas that you might be interested in as well.
With that being said, here's my advice for you. In high school, you should try to take advanced placement science classes. AP Biology and AP Chemistry are good examples. Although you can't take the credit in college, it'll be a good introduction to your college classes. You should probably take these during junior and senior years (I'm taking APC in senior year, FWIW). The introduction to healthcare class is a good idea, as you'll get a taste of whether healthcare is a good fit for you.
Take classes that interest you and pay attention to your grades. The biggest thing with high school is to get into a good undergrad college. Your pre-med work won't' begin until undergrad anyway. Enjoy the time you have (and I can't emphasize this enough). One of the things I regret looking back is not getting involved in as many things. I'm going to make up for it in college, but you should do it now. Join a club or two that you're interested in. It'll look good for your resume, and it'll be a good way to stay unstressed and maintain a grip on your social life.
Remember that I'm only a high school senior, so I'm not the best resource for medical school or anything like that. I'd be more than happy to answer questions about high school or college applications (undergrad only) if you have anything else. Good luck!