At a lot of law schools, the employers come looking for the students, but that's not to say that merely being a law student makes you an in-demand commodity. Most law schools will organize a sort-of job fair, inviting dozens of prospective employers to set up a table and conduct preliminary interviews with their students. This enables law firms and government offices to get a head-start in cherry-picking the top students, but it also lets the students learn a few things about the law firms, as well as get some trial-by-fire experience in being interviewed.
These job fairs usually take place right at the start of the academic year. Importantly, they serve as the prelude for the formal interviewing process that will occur later in the semester. Students sit for “early interviews” so as to get themselves in the hopper for the real interview cycle.
The early interviews generally last around 15-20 minutes. Most schools will devote a couple of days at the start of the fall term for their early interviewing program; many schools devote an entire week. Students should expect to sit for several interviews a day … and for several days. It's like speed-dating, only you're trying to get your first job, not get to first base.
Is it a definite that you will find your ultimate employer during the early interview program? No – some employers don't send a representative to every law school, although just about all of the “major” firms and governmental agencies do so. But if a firm did send a representative to your school's program, it is harder to ultimately get a job with that firm if you didn't sit for them during for an early interview.
After this early interview period, jobhunting is done in conjunction with the law school's Placement Office. The Placement Office is both a clearinghouse for job listings (law offices send notices of their openings here), as well as a resource for job hunting advice.
The best thing that you can do for your career once you get to law school is to get to know the people in your school's Placement Office, and to do so right away. Even if you just walk in to introduce yourself to a counselor, and ask them what you need to be doing, that's a good start. In fact, don't be afraid to ask them if there are any questions that they think you should be asking. Remember, you are entering a brand new environment, and you really don't know how things work, what is considered important, etc. Finding out what you need to ask is just as important as finding out the answers.