When your water pump leaks it is due to the seal erroding. You can just replace the seal but it is not recommended to do so. When you buy the waterpump it will come with a new gasket/seal. And it is usual to replace the cambelt etc at the same time.
Well first make sure the pump itself is not the problem. If so get a new one. Buy a new gasket set also. Then drain your coolant down and remove all accessories in front of the pump and then remove the pump and clean off the old gasket. Install the pump and torque to specified amount then revere the process.
You will need to take it in and have it checked. Or get a manual at the auto parts store with the make and model of your car. It will tell you how to fix it.