I do Social Work and have a Bachelor’s degree in Psychology. Hopefully I will be able to offer you some useful information. First may I say that it is a very honorable career choice.
Now when you graduate high school you choose a major in college. Very few colleges have a major in social work at the undergraduate level. If the college of your choice does not have this major ones that would work toward a social work degree are psychology and human services. Other programs like ethnic studies or sociology might also work towards social work. So your first step is figuring out what you want to major in. Take a look at the colleges you’d like to go to and see which degrees they offer that are similar to social work (if they don’t have an actual social work program). You can then look to see what classes are needed for that degree and apply that to your high school curriculum. You do not have to decide on a major to get into a good college, sometimes it is useful however.
In general though it does not matter which classes you take in high school. It is more important to get good grades, good letters of recommendation, do good on your SAT/ACT which all focus on general studies and not specific classes. Social work does require a lot of communication skills so writing and literature can be helpful. It also requires cultural understanding and empathy so electives that have to do with cultural studies or contemporary issues are also relevant.
You should also start doing some volunteer work in your community. This will help you significantly when applying for college and it will also give you some necessary experience.
To research colleges you should write out a list of criteria. What aspects of college are most important to you. Location, What Majors they Offer, How beautiful the campus is, teacher to student ratio, if they have a population that is diverse, do they have dormitories, do they offer good scholarships etc… For most people location is a primary indicator. For many others it is the campus atmosphere (liberal vs. conservative or party vs. non-party etc..). Once you make your list you can do google searches such as colleges in oregon, liberal colleges, etc…
You also want to consider the admissions requirements of each college you are interested in. This is quite easy to find on a college website. See if you meet their criteria or not.
To research social work more you should do some good google searching and reading. But you should also chat with some social workers to get a more personal perspective.
If you have any more questions I will happily answer. Or if you need me to clarify anything I said so far.