first identify where water is coming from you may need a rubber seal. turn water off from under sink after you find source of leak then unscrew handle that says hot or cold. BUT check water before you turn it off to see it it is hot or cold. If it is dripping cold water it is the cold line. take cold water knob off then unscrew the valve (AFTER YOU TURN OFF COLD WATER SIDE OFF FROM UNDER SINK) take valve out look on the bottom of valve there is a rubber seal if it is damaged unscrew the screw in the middle of the rubber seal take it out their is a number on one side write it down any hardware store knows these numbers they will give you the same one some times you can but one or they come in a pack (Inexpensive).
Replace your leak should be over (CHANGE THE OTHER SIDE IF YOU STILL LEAK) good luck