'It' and 'there'

His father has just retired. > He was a teacher.

I'm waiting for my wife. > She is late.

Go away. (You forbid someone to enter)

Play it again, please. (You request someone to play it again)

Where or when something is

A number or amount

Something existing or happening

There's an interesting book on the shelf.

There'll be an eclipse of the moon tonight.

There is plenty of bread left.

There were twenty people at the meeting.

There's a small problem.

There was a nasty fight.

It's nearly one o'clock.

It's my birthday.

It's raining.

It's a lovely day.

It was getting cold.

It's great living here.

It's nice to meet you.