I have a leak in one of the faucets in my bathtub. It wasn't leaking, I turned it on to take a bath, when I turned it off, it started leaking.
I have no idea what to do.
You need to turn off the water at the meter and disassemble the valve. If the valve is an old style, the rubber compression washer may have come loose or deteriorated. Also, check the seat for wear or chinks. If the valve is a new style, a grain of sand or other debris may be jammed in the small valve openings and can be blown out or, if damaged, the valve can be replaced. All of these repairs are easy to do if you know how. Get a book from the hardware store or the library. Try Readers' Digest "Fix-it-yourself Manual".