Usually, this is caused by a worn-out washer. Remove the handle and packing nut, extract the stem and replace the washer, then reassemble it in the same order.
to fix you have to turn off the water mains first, turn the tap on so that all of the water is gone and then simply replace the gasket by taking of the tap handle.
most faucet under the knob will be washers you can replace those maybe even just tighten down the placment screws in faucet if this dont work get a new faucet