There
When we talk about something for the first time, we use there to say that it exists
There is some jam in the cupboard.
There is a lot of traffic on Conway Road today.
There has been a significant change in the weather.
It
We use it to express a certain fact or situation
There is come jam in the cupboard, it is very nice.
There is a lot of traffic on Conway Road today, it seems to be getting worse every week!
There has been a significant change in the weather, it never used to be this cold in May.
There also means to/in that place
Look at that amazing mountain, I want to go there.
He always said that he wanted to visit the new supermarket on the high street, I think he was going there.
I know that you would like to talk about what happened a few years ago, but please do not go there! [please do not talk about this situation]
There is used to communicate a prediction or certainty
There must be a way of stopping this problem from getting worse.
There is going to be trouble!
There will be complaints when people hear about this.
We use it to say things like the following
It is not a good idea to wake up at 3am to practise English.
It is going to be very sunny today and I suggest that you use some sunblock.
It is better to have a takeaway on Fridays as it is the end of the week.
We use it for distance, time and weather
Wow, it is 6pm already, I better be going.
As it is Tuesday, Sally will be organising a meeting between between all the managers.
It is a very cold day, why are you not wearing your hat?