Start out with a love of books, information, information media, or whatever all this info stuff is called these days.
You need academic training and credentials, starting with a bachelor’s degree—or anything—and for the truly dedicated, a master's degree in library science. If you can't get enough of book learnin', you can spend a lot more years getting your doctorate, but that's if you want to spend your life teaching and making the lives of your graduate students miserable.
There are the specialists, though. Law librarians, elementary and secondary schools librarians. And their ilk. There's more school in the offing: law school for the law types, teaching credential school for the teacher types. You get the picture.
Also some states make librarians get certified, meaning more study, more tests. Getting trained, o future librarians, is no walk in the park, but for the truly dedicated, it's all worth it. You will become an impresario in the world of information.