A crew is an organized group of workers. A crew might keep a ship sailing smoothly or pave a road smoothly. Either way, crew implies cooperation among workers.
If you're hired as a member of a ship's crew, it will be your job (along with the other crew members), to keep the boat running smoothly, and the passengers happy and well-fed. Crews are usually a group of people who work together on a ship, airplane, or movie — but the word is also a slang term for a group of friends who hang out together — like a crowd or posse.