There is - There are - There was

There is

There is significa "hay" (presente, singular) y se contrae como There's.

     There's a big black cloud on the horizon.

There is se utiliza también para sustantivos incontables.

     I think there's some sugar on the top shelf.

Ahora vamos a ver el negativo de There is. Se puede contraer de dos maneras: There isn't o There's not.

     There isn't anything to read in this house!

     There's not a single person in this village!

Y ahora veamos el interrogativo.

     Is there a chemist's near here?

     Is there any ice on the roads?

Continuemos con el plural (ver There are, a continuación).

There are

There are significa "hay" (presente, plural). En afirmativo no existe contracción posible, sólo en negativo y se contrae como There aren't.

     There are hundreds of flies fliying about!

     There aren't any zebra crossings on my street.

Y ahora veamos el interrogativo.

     How many left-handed people are there in your neighbourhood?

     Are there many fax machines in your office?

Continuemos con el pasado (ver There was, a continuación).

There was

There was significa "hay" (pasado, singular) y no se suele contraer.

     There was a big fat fly on his computer screen.

     There wasn't any tea left in the tea-pot.

Ahora veamos el plural, que se forma así: There were o There weren't.

     I don't know if there were that many people there.

     There were fifty mistakes in the text.