THERE IS  -  THERE ARE
(HAY)
When do we have to use them?

There is
 It is used to say something in singular.
Ex: There is a pencil in my bag.
(Hay un lapiz en mi cartera)

There are
  It is used to say something in plural.
Ex: There are two hospitals in my town.
(Hay dos hospitales en mi ciudad)


To make interrogative sentences, we do it as follows:

Is there an apple on the table?
(¿Hay una manzana encima de la mesa?)

Are there two cinemas in your town?
(¿Hay dos cines en tu ciudad?)


To make negative sentences, we do it as follows:

There isn´t a computer in my room.
(No hay un ordenador en mi habitación)

There aren´t two train stations in my town.
(No hay dos estaciones de tren en mi ciudad)