Before you get involved with most plumbing projects, you'll need to shut off the water flowing to whatever you're working on. Most of the time, there are easy-to-access gate valves or compression valves that you can turn with your hand. Turn them clockwise all the way to turn off the water and counter-clockwise to turn it back on when you're done. For sinks, look under the sink and you'll usually see two valves—one for hot water and one for cold. On kitchen sinks, you might also see valves for the ice maker on your fridge or your dishwasher. Just turn them all off. For toilets, the valves are on the wall or right on the pipe behind the toilet.
The word "plumber" dates from the Roman Empire. The Latin for lead is plumbum. Roman roofs used lead in conduits and drain pipes and some were also covered with lead, lead was also used for piping and for making baths. In medieval times anyone who worked with lead was referred to as a plumber as can be seen from an extract of workmen fixing a roof in Westminster Palace and were referred to as plumbers "To Gilbert de Westminster, plumber, working about the roof of the pantry of the little hall, covering it with lead, and about various defects in the roof of the little hall". Thus a person with expertise in working with lead was first known as a Plumbarius which was later shortened to plumber.