Hay

There is, there are

Hay is a very common Spanish expression. It is equivalent to the English expression "there is" or "there are:"

Hay un libro en la mesa.		There’s a book on the table.
Hay tres hombres en la clase.		There are three men in the class.
Hay muchas cosas a hacer.		There’s a lot to do (There are lots of things to do).

Hay is the present tense impersonal form of the verb haber, and can be followed by a singular or plural noun.

In other tenses and moods, the impersonal verb haber has both singular and plural impersonal conjugations, but most Spanish speakers consider use of the plurals as incorrect. I’ve provided both forms here for reference.

conditional	habría		there would be
	habrían		there would be
future	habrá		there will be
	habrán		there will be
imperfect	había		there was
	habían		there were
present perfect	ha habido		there have been
	han habido		there have been
pretérito	hubo		there was
	hubieron		there were
subjunctive	que haya		that there is/are
	que hayan		that there are

Hay que

When followed by an infinitive, hay que means "it is necessary to" or "one has to:"

Hay que estudiar cada día.		It’s necessary to study every day.
Hay que trabajar para triunfar en la vida.		One has to work in order to succeed in life.