1. Ask questions characterized by existence:
¿Hay alguién aquí? (Is there someone here?)
2. State the existence of something:
Hay pan fresco en la cocina. (There is fresh bread in the kitchen.)
3. State abroad “impersonal” obligation (lacking a specific subject, sometimes translated into English as “one”) in the form of hay + que + infinitive:
Hay que luchar por la vida. (One must fight for one’s life.)
Hay que comprar más vino para la fiesta. (It is necessary to buy more wine for the party.)
4. Hay can be used in different tense:
El año pasado hubo menos accidentes de tráfico (Last year there were fewer traffic accidents.)
Antes había menos contaminación en las ciudades (It used to be less pollution in the cities.)
HABER vs ESTAR
There is an important distinction to be made regarding hay and other verbs with similar uses. It is easy to confuse “hay” with forms of ver “estar” to be. It is best to distinguish them by noting that whereas estar expresses the position or location of someone or something, hay refers to that someone’s or something’s very existence. Compare:
Está en casa. (He is at home.)
Hay alguien en casa. (There is someone at home.)
Anyway, you can learn more about this topic by clicking on the link HAY vs ESTAR.
HABER vs TENER
There is also a tendency to confuse HABER with TENER because both are translated in English as “to have”. Remember as we mention above TENER is used to express possession and can NEVER be used as an auxiliary verb (unlike Italian and Portugues).
Tengo una moto (I have a motorbike.)
He comprado una moto (I have bought a motorbike.)
Hay muchas motos en la calle (There are many motorbikes in the street.)
It is also easy to mistake “hay que” within “tener que“ + infinitive phrase. Remember that while both express an obligation, tener que . . . has a specific subject (and tener is conjugated according to that subject), whereas the hay que . . . construction expresses an obligation not specifically assigned to a particular individual. Compare:
Hay quecomer mucha fruta. (Someone or everybody should eat fruit.)
Tengo que comer mucha fruta. (I have to eat a lot of fruit)