There is / there are ("hay")

Un "hay" con dos formas

Para decir que algo existe o está en un lugar, el inglés usa there is con singulares e incontables, y there are con plurales. El español tiene una sola forma ("hay"); el inglés concuerda con lo que viene detrás.

Español	Inglés
Hay un problema.	There is a problem. / There's a problem.
Hay dos habitaciones.	There are two bedrooms.
Hay leche en el refrigerador.	There is some milk in the fridge.
Hay mucho tráfico.	There is a lot of traffic.
Hay muchas personas.	There are a lot of people.

En una enumeración, el verbo suele concordar con el primer elemento: There is a sofa and two chairs. (Hay un sofá y dos sillas.)

Negación y preguntas

There isn't any milk. / There is no milk. — No hay leche.
There aren't any free seats. — No hay asientos libres.
Is there a pharmacy near here? — ¿Hay una farmacia cerca de aquí?
Are there any questions? — ¿Hay alguna pregunta?
How many people are there? — ¿Cuántas personas hay?

Respuestas cortas: Yes, there is. / No, there isn't. / Yes, there are. / No, there aren't.

Pasado y futuro

Tiempo	Singular	Plural
pasado ("había", "hubo")	There was a party.	There were many people.
futuro ("habrá")	There will be a meeting.	There will be changes.

There were a lot of tourists in the city. — Había muchos turistas en la ciudad.
There will be a test on Friday. — El viernes habrá un examen.

there is o it is

There is presenta algo nuevo; it is habla de algo que ya se ha mencionado:

There is a letter for you. It's from the bank. — Hay una carta para ti. Es del banco.

Ojo si hablas español

"Hay" y "había" invariables. ✗ There is many problems. / ✓ There are many problems. ✗ There was a lot of people. / ✓ There were a lot of people.
Frase sin there. ✗ Is a bank near here. / ✓ There is a bank near here. ✗ In my city are many parks. / ✓ In my city there are many parks.
"Hay que" + infinitivo. No se traduce con there, sino con un sujeto y have to: ✗ There is to wait. / ✓ We have to wait.

Diálogo de ejemplo

Is there a bank near here? — ¿Hay un banco cerca de aquí?
Yes, there are two on this street. — Sí, hay dos en esta calle.
Is there an ATM too? — ¿Hay también un cajero automático?
Yes, there's one next to the pharmacy, but there's always a long line. — Sí, hay uno al lado de la farmacia, pero siempre hay una fila larga.