A. There and it'
We use there... when we talk about something for the first time, to say that it exists:
* There's a new restaurant in King Street. (not 'A new restaurant is in King Street')
* The journey took a long time. There was a lot of traffic. (not 'It was a lot of traffic')
* * Things are much more expensive now. There has been a big rise in the cost of living.
It = a particular thing, place, fact, situation etc. (but see also Section C:
* We went to the new restaurant. It's very good. (it = the restaurant)
* 'Was the traffic bad?' 'Yes, it was terrible.' (it = the traffic)
* I wasn't expecting them to come. It (= that they came) was a complete surprise.
Compare:
* I don't like this town. There's nothing to do here. It's a boring place.
Note that there also means 'to/at/in that place':
* The new restaurant is very good. I went there (= to the restaurant) last night.
* When we arrived at the party, there were already a lot of people there (= at the party).
B. You can say there will be, there must be, there used to be etc.
* Will there be many people at the party?
* 'Is there a flight to Paris this evening?' 'There might be. I'll phone the airport.'
* If people drove more carefully, there wouldn't be so many accidents.
Also: there must have been, there should have been etc.:
* There was a light on. There must have been somebody at home.
Compare there and it:
* They live on a busy road. There must be a lot of noise from the traffic.
They live on a busy main road. It must be very noisy.
* There used to be a cinema in King Street but it closed a few years ago.
That building is now a supermarket. It used to be a cinema.
You can also say there is sure/certain/likely to be something (see also Unit 64E):
* There is sure to be a flight to Paris this evening.
C. We use it in sentences like this:
* It's dangerous to walk in the road. (It = to walk in the road)
It is unusual to say 'To walk in the road is dangerous.' Normally we begin with It...
* It didn't take us long to get here. (it = to get here)
* It's a pity (that) Sandra can't come to the party. (It = that Sandra can't come)
* Let's go. It's not worth waiting any longer. (It = waiting any longer)
We use it to talk about distance, time and weather:
* It's a long way from here to the airport.
* How far is it to the airport?
* What day is it today?
* It's a long time since I last saw you.
* It's going to be a nice day.
* It was windy. (but 'There was a cold wind.')