A hospital is the place to go when you're very sick or injured in a way that requires immediate treatment. If you trip over your shoelaces and break your arm, you'll need to go to the hospital.
People having surgery or delivering a baby usually go to a hospital, and if you suspect you have food poisoning, you might visit the emergency room of a hospital. Hospitals are staffed by doctors and nurses, as well as office workers, cleaners, and aides of various kinds. The earliest hospitals were shelters or needy people, or hostels for travelers, and the word comes from the Late Latin hospitale, "guest house or inn."