Some clauses begin with the introductory words THERE or IT rather than with the subject of the sentence. These introductory words are sometimes called expletives. The expletive THERE shows that someone or something exists, usually at a particular time or place. These sentences generally follow the pattern there + verb to be + subject:
There are many skyscrapers in New York City.
There was a good movie on television last night.
The expletive IT is used in a number of different situations and patterns:
It is important to be punctual for appointments.
(with the verb to be + adjective + infinitive)
It was in 1959 that Alaska became a state.
(with the verb to be + adverbial + noun clause)
It takes a long time to learn a language.
(with the verb to take + time phrase + infinitive)
It was David who did most of the work.
(with the verb to be + noun + relative clause)