Primary duties of a hostess are taking care of the cleanliness and tidiness inside of the boat, and, if there is no chef, she is also in charge of preparing meals.
Since there is always lots of work to be done around the boat to keep everything in order, every task must be properly delegated between the crew.
So, the tasks of the hostess are vary depending of whether she is the alone on board or with other crew members.
If you hire only a hostess, she is in charge of keeping the boat tidy, cooking and groceries shopping, making breakfast… In this case, your duty is to navigate the boat and take care of the security of everyone on board as well as the boat itself.
If there is a skipper with the hostess on board, the two of them will take care of most things that must be done. Generally, we could split their tasks: he is managing the exterior, and she is in charge of interior, but that is little blunt. She will help him to anchor in marinas as well as with some minor repairs on the deck (if necessary).
If the hostess is a member of full crew, she is usually not in charge of groceries shopping or any other physical work.
She cleans, tidies up the place, sets the table, serves the food... She is also here to answer all of your questions and help you with an advice. She is constantly communicating with the guests and you can ask her if you have any kind of a problem. Hostess are, in the most cases, educated and well informed with the recent events, so they can help you, answer on your questions, and explain lots of things regarding the local rules and traditions.
Your duty is to assure her the place to sleep and provide food.