Positions
Counselor - Even in space people need a shrink. A counselor is a multi-purpose position, allowing crewmembers a place to go and discuss their problems. Counselors are also charged with ensuring everyone on the ship is crazy. The moral of the crew also falls under the counselor.
Engineering - Things break, all the time. If it isn't something breaking, the Captain always has some strange request for a flux inverter. As well as their duties aboard their ship, engineering is also used in reconnaissance on alien technology.
Medical - Did you get tennis elbow in the Holodeck? Trip and break your arm? How about take a phaser blast in a fire-fight? Well, it is medical officers job to keep you healthy and in one piece. The oddest part is that they do it all with the same tool . . .
Operations - Operations deals with the day to day operations of the entire Starship. They are involved compiling sensor data, determining power routing, handling communications, transporters and keeping away teams on a transporter lock and much much more. They serve the ship in the most diverse position and are a key to almost everything happening.
Science - If it wasn't for science, Starfleet wouldn't even be out in space right now, and OPC wouldn't be on this planet. From data collection, to running tests, to helping engineering with the more tricky conundrums, Science is a very important aspect of any crew.
Security -Security keeps the ship safe and protected. They make sure that order is maintained and internal security is kept.
Tactical - Tactical works with Security and make sure that not only the ship is protected but the quadrant. They man and maintain the weapons and defenses of the ship. They protect the ship in all situations.