Awesome!!!! Thank you for your interest in joining the worlds greatest Navy. I myself was active duty for 15 years, My wife was for 20 and my brother for 22. So as you can see I am really passionate about this. To answer your question the classes you would need to take honestly would depend on what you want to do in the Navy. Keep in mind that there are tons of career choices. Cyber Security, Legal, Cooks, to weapons. The possibilities are endless. I would suggest that you do as well as you can on the ASVAB test which is the Armed Services Vocational Aptitude Battery. It is used to test you and discover the jobs you would be best suited for. Scoring high gets you more options so you really want to focus on that. Online there are study guides that will give you an idea what you should be looking for in term of study. 4tests.com is one site you may want to look at. Hopefully this helps you and keep in mind that you should look at a job that you can transition to once you decide to leave military life. The military provides all the training you need for your future job and often that will give you all the skills you need once you decide to become a civilian again. Good luck.
For both, do your best academically in your high school classes, maintain your physical fitness, and avoid any disciplinary actions from your high school.
To enlist, you will have to take the Armed Services Vocational Aptitude Battery (ASVAB). You score on the ASVAB will open up certain rates (enlisted job positions) to you. There are ASVAB prep books and even prep classes if you want to work on raising your score for a specific rate.
To enter as an Officer, a college degree is required. There are many Officer programs such as Navy Reserve Officer Training Corps (ROTC), the Naval Academy, or Officer Candidate School (OCS). The major difference between ROTC and the Naval Academy over OCS is that both enable you to graduate college debt free (or close to debt free) as ROTC programs typically provide a full scholarship leaving you to fund housing and living costs and Service Academies are free to attend. In ROTC and at the Naval Academy, you complete your college coursework while you complete your military training, where as at OCS, you attend after attending and graduating college as a civilian student.
Meighan recommends the following next steps:
I was active duty Navy for 9 years, and I can confidently say that Kenneth is absolutely correct - scoring well on the ASVAB is what unlocks various career paths in the Navy. There are a ton of options for Navy careers. You should look at this website, which explains the various jobs: https://www.navycs.com/navy-jobs/
Once you've got a couple that you're interested in, talk to your Navy recruiter. They can give you some more in depth information about your prospective field. The Navy will teach you everything they need you to know, both in formal classrooms and on the job training, but more education is never a bad thing. When you've figured out which direction your job interests lie, you should be able to figure out what classes you need to give you a leg up in your chosen career.
Chris recommends the following next steps: