Hmm, you will get a variety of replies, I'll be the first of this sort:
1) Use the search function at the top of the browser. There are plenty of threads that will answer your questions.
2) You are a sophomore in HS, set on going to medical school. My advice is this: medicine is more or less a lifetime commitment. Do not go into this blind. Do ECs that will give you an idea of what the rest of your life could be like. Do not sacrifice fun for a mere line on an application. I'm a strong supporter of the "don't rush though school, focused on picking up ECs that you think will wow the adcoms." IMHO you are totally throwing away the 4-5 best years of your youth. Whatever you do, be interested in it, and passionate about it. As total anecdotal evidence, it seems to me that adcoms can see that an applicant has become well rounded by sincerely following their desires though college. Don't be that guy/girl who does things just to say they've done them. Do what you enjoy with audacity, and you will have a killer app.
