Hiya Annie, Using a rag or toilet paper, dry all of the stop cock.
Once it is dry, try to assess where it is dripping from. Usually they leak from a small nut called a gland. If you look at the stop tap you will probably find on the spindle (the long narrow bit) attached to the body a 'small' hexaganol nut. Firsly choose the correct size spanner and place it on the nut. Applying pressure ( clock wise) tighten it. If the gland is already 'very tight,' then you need to undo it (anti clockwise) and wrap some PTFE tape around the gland thread. Then tighten it again (clock wise.)
Be warned Annie, that if you don't judge things correctly you will make the drip a lot worse But, this procedure is a job we would give to an apprentice to fix. Good Luck..Don't drown.. ps. paste the address below in to your header and follow the instructions on the page. http://www.ultimatehandyman.co.uk/stop_tap/re_Packing_a_stop_tap_gland.htm
Bucket head.
December 2010