THERE/IT

Some sentences have "There" or "It" as a subject to start a sentence. 

It is always followed by a singular verb.

1. It is a hot day.

2. It was Saturday.

We use "It" when talking about weather or time.

"It" can also be used to introduce a phrase or a clause.

1. It is useful to buy this dictionary. 

2. It was foolish that you behaved like that.

"There" can take a singular as well as a plural verb.

It depends upon the real subject which comes after the verb.

If the real subject is singular, the verb is singular.

There is a mobile on the dining table. 

If the real subject is plural, the verb is plural. 

There were bangles in the drawer.