Like the Electrician is to electricity, a Plumber is to the water running through the pipes at home. A Plumber can not only free pipes when the water isn't running properly, but also install a Water heater, toilets, bathtubs etc. Some things can be done by yourself, for example when the water is not running properly down the sink. You can open the sieve or one of the external small pipes and clean it. But for bigger things, it is better to contract a professional. Here you can read more about plumbers and plumbing types.