'It' and 'There' as dummy subjects
English clauses always have a subject:
- His father has just retired. > He was a teacher. (NOT Was a teacher.)
- I'm waiting for my wife. > She is late. (NOT Is late.)
except for the imperative:
- Go away.
- Play it again, please.
There
If there is no other subject, we use there to talk about:
- where or when something is:
- There's an interesting book on the shelf.
- There'll be an eclipse of the moon tonight.
- a number or amount:
- There is plenty of bread left.
- There were twenty people at the meeting.
- something existing or happening:
- There's a small problem.
- There was a nasty fight.
It
We use it to talk about:
- times and dates:
- It's nearly one o'clock.
- It's my birthday.
- the weather:
- It's raining.
- It's a lovely day.
- It was getting cold.
- We use it with the verb be and an –ing form or to-infinitive to express opinions
- It's great living here.
- It's nice to meet you.