First you'll need to attend some sort of college or university to start your undergraduate degree. There are specific classes you'll need to take in college for vet school. You will also need to get veterinary and animal experience (contact a vet and ask about shadowing them). You can find a list of the classes you'll need to take in college to get into vet school if you search for US vet schools and then look up the classes each require (different schools require different things). But your first priority should be starting college! You'll most likely have an advisor at your college or university and they'll be able to help you with this as well to understand the basics of getting into vet school.
Your high school grades will only matter for getting into undergrad, but even if you did very poorly in high school you can still most likely go to community college to start out.