A crewed charter is a boat rental that comes with a captain and usually a crew. How many crew members there are, and in which roles, depends on the size of the boat. You are a guest on board: the crew sails the boat and looks after you.
What does the crew do?
Depending on the boat, the crew sails and navigates, cooks, cleans, serves and hosts. You do not have to worry about any of it, and you need no sailing experience or license.
How is it different from hiring a skipper?
On a crewed charter, the crew belongs to the boat. The charter company usually employs them for the whole season, so they know the boat and its systems well. That is different from renting a boat and hiring a skipper or crew for it separately (see How do I hire a skipper or entire crew for my yacht?).
Who is a crewed charter for?
For anyone who wants to relax completely on the water, and for groups without sailing experience. Borrow A Boat offers bareboat, skippered and fully crewed charters: Do I need to bring my own captain/crew?
Tipping the crew is customary on a crewed charter. The usual guideline: Do I need to provision the skipper/crew?