Social work is a very versatile career. Some social workers assist patients during hospital stays, others serve as counselors in high schools or colleges, many work with disadvantaged families to help them with their child-rearing, housing or employment needs, some have "private practices," just like doctors do, to advise patients who are experiencing personal problems. The list of duties that social workers perform is seemingly endless.
This site, below, sponsored by the U.S. Department of Labor, will give you a good overview of the profession and the many types of social work you can do.
1) Enroll in a college that offers the Bachelor of Social Work degree (BSW) that you can complete as an undergraduate (i.e, usually within four years). Not all colleges have a BSW major. However, most will offer a related field like sociology or psychology. These are good majors for you if you expect to go on to graduate school and earn an MSW (More on that in a minute). However, if you think you want to go to work in your field after only four years, then you should look for a college with a BSW program. But note that BSW positions are usually low paying and often don't offer a lot of options for promotion. If you seek a career in social work, I highly recommend that you continue your schooling and earn a Master's degree. (See below.)
2) Earn a Master's of Social Work (MSW). This is a degree that usually requires that you attend college for four years to earn your Bachelors degree and then continue for one or two more years afterwards to earn the MSW. That may sound like a lot of schooling, but once you have your MSW, you'll find that you will have MANY more job options than social workers do who hold only a Bachelor's degree.
If you plan to study for an MSW, you can choose a wide range of undergraduate majors in college, even those that don't seem related to the social work field. Regardless of the major you choose--and depending on the type of social work that interests you--undergraduate courses in psychology, sociology, law, criminal justice, biology (for medical social workers), foreign language (especially Spanish), women's studies or gender studies, etc. will also prove useful.
Once you have completed your education, you will find different licensing requirements, depending on the state in which you live and the type of social work you wish to do.
Hope that helps. Good luck as you plan your education and career.