Basically, they were the ones who ran the ship. Stokers fed the boilers, the engineers kept the engines running and managed things like the generators which provided power, the stewards tended to the passangers and their wants/needs, the officers navigated the ship, etc....
Is there anything in particular you're looking for? For a question as broad as this, specifics might be a bit more helpful.
As Michael says, it would help to know what you are looking for. The people who use this sight have an enourmous amount of knowledge about the ship and her crew. For example, most of the crew lived in Southampton. Many people from there died. How about picking some examples of crew members and then using the site to put a pen picture together of the person and their role on the ship?
yes gloria, as ian and michael say, all of the crew had their own duties to perform. i am a crew member myself aboard a ship. when you go on board, you sign a muster list. this is to specify which position you would take up should an emergency situation arise. for instance, i am in charge of first aid, so i would need to go to the bridge for the equipment and take it to my designated location. the muster list is to specify where each crew member should be and what they should do when they get there. firstname.lastname@example.org