They apprentice for years before they get to take responsibility for a sizable production.
The director, too, has assistants, starting with, obviously, the assistant director. But while the @A.D. reports to the director, he or she is actually not really a directorial apprentice. Assistant directors don't get to do much -- if any -- directing; they're more on a track toward becoming a production manager or a producer. They break down the script, scene by scene, according to location or set or actors' calls (that is, what actors will be needed for shooting the scene). Then they put together a shooting schedule to get the most done in the least possible time with the most efficient use of people, money, and equipment. A good A.D. can save a production hundreds of thousands of dollars just by analyzing the script before it's shot and finding the best way to schedule the production itself. It's an incredibly demanding job, and because it relies so much on good communication between director and assistant, most directors will try to book their favorite assistants as much as possible.
Then there's the second assistant director, essentially the A.D.'s assistant; he or she's responsible for crew and cast calls; for keeping track of how many hours the crew has been on call so as to minimize overtime; sometimes for helping to cast extras when they're needed in a scene and then cueing them to move, stand, sit, or run as required; and for working with cops and security to keep the shooting location free from disturbances. And if you've noticed, on big productions there are, yes, second second assistant directors, whose job, as you might guess, is to assist the second assistant director.
When it comes to post-production, the titles seem to breed faster than rabbits. Most are self-explanatory, but you should know that a Foley artist is the person who creates and matches special sounds to the images on the screen. For example, in "@Monty @Python and the Holy @Grail," we see King @Arthur riding his invisible horse around England.
