Burst water pipes can be a real plumbing emergency, potentially leaking gallons of water all over your house. Your best bet would be to pick up the telephone and call an emergency plumber to come out and fix the situation, however there are a few things you could do to improve the situation:
Find the water supply to the leaking pipe and shut it off. If you are not sure where this is located shut off the water supply to the entire house. It is vitally important that anyone living in the house knows where the water shut off valve is and how to use it should a situation like this arise.
Once the water supply has been shut off turn on the cold water taps to drain the system of cold water.
Turn off your water heater and/or central heating system.
Turn on your hot water taps to drain the system of hot water.
A pipe leaking water can be extremely dangerous around electrical outlets and appliances so it would be wise to turn off the electricity at the mains until the situation is resolved.
Once you have found the damaged pipe and turned off the water supply you will need to either repair or replace the damaged section of pipe. Unless you are competent and confident at repairing pipes you will want to enlist the services of a professional plumber.