While I'm not an AB myself, I've worked on ships alongside them, so I've gotten a lot of insight into how the crews work.

The short answer is that it depends on your role. Basically, there are usually three or four types of crew on any ship:

• Bridge
• Deck
• Engineering
• Anyone else (me), on more specialized ships.

Bridge:
Responsible for the navigation, safety, comms, scheduling, and all procedural tasks with running a ship. There are always someone on the bridge at all times, and this person is in charge of everything. The captain is of course the senior officer, but his responsibility and authority is delegated when he's off duty.

Deck:
It can be pretty chill, but there's still a fuckton of tasks to do. Painting, chipping rust, inspections, maintenance, helping out bridge/engineering if they need it. Most people on the bridge or in engineering have been Deck crew (AB - Able-bodied Seaman) at some point.
I've also seen deck crew being responsible for grilling on Saturdays.

Engineering:
Everything to do with the engine, and overall mechanical functionality of the ship.

I intentionally left out the galley staff, as this varies a lot between ships. When it's a big crew, like the ships I've been on, there's a dedicated galley staff. On smaller crews, it can be the ABs' job to serve up meals.