Criminal Prosecutors as a career?

What does this job entail, because it can't be as easy as it seems on Law and Order. The basics seem clear enough; work with cops, build a case, and try to prove the person guilty. What else is there? Is getting the job hard, besides Law School and the BAR? Any jobs in the military, particularly in the Marine Corps? Thanks, and pardon the spelling, I'm doing this all on my iPod.