it depends.
If an expedition ship, there will be a briefing the night before to cover what your going to see the next day. Also the expedition staff are full of knowledge and when walking around the ship, they will spot birds and tell you all about them. Some will be out at night and explain the night sky to you.
If a standard cruise, the theater will be used on sea days to provide you with history and suggest places you should visit when the ship docks. Also will provide where to go if your in to shopping.