Paralegals work for lawyers. They do almost everything a lawyer does, except they do not set fees or give advice. Think of it as a highly advanced administrative assistant, specializing in law. They research legal issues, draft documents (everything from wills to appellate briefs). Proofread the lawyer's work, greet clients, do intake, answer phone calls and correspondence, file documents with the courts (mostly electronically now days), index and review documents, file discovery, respond to discovery, and possibly most importantly, stay up to date on the calendar (deadlines for all the various stages of the cases). They often times have to "run interference" for the lawyer when certain clients keep calling and calling. They help prepare for trial, put trial notebooks together, organize exhibits, schedule court reporters for depositions, arrange travel for the lawyer or for witnesses coming in from out of town. If you work for a solo practitioner, you might also be expected to run errands, such as picking his laundry up from the cleaners or getting his car serviced, and keep the coffee coming. The hardest part is often putting up with the lawyer, as they can be a difficult bunch to work for. They tend to wait until the last possible minute to do things, and then rush around all stressed out trying to get it done. If you work for a big firm, you are likely to specialize in one particular area. Most recent graduates do not go straight to work for big firms, you have to work your way up.
People used to enter the field without formal education, but that is not happening so much any more. You can get a certificate, 2-year degree, 4 yr degree, or even a graduate degree. Some paralegal studies programs are ABA approved, some are not. I would encourage you to look at the ones that are. Some of the ones that are not approved do not do a very good job, and they sometimes charge a lot. Stay clear of the private schools that are not ABA approved. Also, please understand, that, like lawyers, there are far more paralegals graduating than there are positions for them. Entry-level salaries are low, sometimes as low as $10/hr. If you do an internship while in school, that might turn into a permanent job. Law is fun, but not for everyone. Paralegal is a way to get to almost "practice law" without having to deal with the stress and expense of law school. Depending on the path you take, wages can get pretty decent over time ($50,000).
Paralegals can also work for the gov't. For example, I deal with many of them when I do open records requests. They have to release public documents, but must make sure not to release information that is confidential by law. there are large offices at state and local levels processing all of these requests.
Good luck to you!