I assume that this is leakage that happens with normal use. I have found that with many single handle faucets, if you push the handle all of the way open, hard over and hold it there, they will all leak.
Turn off the water to your faucet from under the sink. There should be a shutoff down there. Make sure that both the hot and cold water lines are shut off, so that when the faucet is open, no water should come out.
Open up the faucet by removing the handle. Usually this is easily done with a screwdriver. There will be a screw someplace to do this with, although it might be an allen type set screw. Sometimes that screw is neatly hidden underneath a plastic plug.
Pull out the cartridge. Drive to your nearest home center, with the cartridge in hand. Now it will be trivial to find the exact cartridge. If you are still unsure, ask for help.
Buy the proper replacement cartridge, complete with all o-rings, etc.
Replace the cartridge into your faucet with the new one, replacing ALL o-rings, all of the pieces that come with it with the new ones.
Put the handle back on, turn on the water.
If it still leaks, buy a better grade of faucet. I have found that cheap hardware sometimes really does perform like CHEAP hardware.