A charge or fee that a government imposes on a citizen or business is called a tax. Taxes help to pay for the services people (and businesses) receive from the government.
There are many different kinds of taxes—on purchases, property, and income, for example—but all tax money is meant to pay for things that benefit people in society. For example, in many places schools, road repairs, fire departments, and health care for elderly and disabled people are all paid for with money from taxes. As a verb, tax can either mean "impose a tax on" or "put a strain or burden on."