If your water pipes freeze you need to open up the faucets on those frozen pipes to relieve pressure and then if possible find the frozen pipe and use a hair dryer to heat the pipe up and melt the ice in the pipe.
Don't hold the hair dryer in one place but instead move the hair dryer back and forth and if possible hold an aluminum pan or even a gloved hand behind the pipe and move the hair dryer back and forth over the frozen pipe to thaw it out.
You can also pour cold water over a frozen pipe to thaw it out if possible.
A heat lamp pointed at the frozen pipe can also work to thaw the frozen water pipe out.
Just be prepared in case the water pipes do burst and be prepared to shut the water main off or other water valve off if needed.
You should leave your faucets dripping during the cold winter months when it's really cold out to avoid freezing and bursting of water pipes.