The Second Assistant Director serves directly under the First Assistant Director and is their right hand man. Their main function is to ensure that all the First AD's orders and directions are carried out.
Also known as Seconds, they have two main responsibilities: 1) to prepare and distribute a "call sheet" (which states the times for all of the cast and crew) and they manage the whereabouts of all cast members so they can be quickly located when the need arises.
Second ADs might also be responsible for finding extras or "background." This is usually handled by a Third AD or a well trained Set PA, but this can become the Second ADs job if need be.
Second ADs usually serve as a liason between the set and the production office. They're often asked to share information with senior managemment on the status of a particular shoot.
To be an effective Second AD, you must have excellent organizational and time-management skills. You will need to coordinate arrangements and detailed plans.
You MUST have genuinely effective communication and interpersonal skills, because as a Second AD, you are likely to deal with a large number of people.
You MUST pay close attention to detail. Keep in mind, your job as a Second AD is simply to cover for the first AD. So, make him/her look good, then you look good.
What to Expect:
As with most productions, a second AD position is a freelance job. It is often long, grueling work that you must do with a smile on your face, because if the First AD doesn't feel you're legitimately covering his/her back, they won't hesistate to replace you
The best way to get work as a Second AD is to start as a Set PA, or Third AD. You will very quickly learn the ropes and hopefully move up the ladder.
Look into the Director's Guild Training Program at http//:www.dga.org for more information on this field.