ref – https://pediaa.com/difference-between-it-and-this/

Referencing

You can use both this and it to refer back to something that has already been mentioned, BUT there is a difference in usage.

it

Subject and object pronoun

It can replace a subject or object that has already been referred to in a sentence. In this usage, we only use it to refer to an inanimate object or an animal, not a person. It is a third-person singular pronoun.

We use it to refer back to a single thing that has already been mentioned. We do this to simply ‘reference it’.

Look at the cat! It is about to pounce on that poor bird.
Please pick up the book on your way out. It is on the table.

It can be used as a dummy subject when talking about the weather, time and distances.

It is really hot today.
It’s ten o’clock.
It is a long way to Los Angeles from here.

You can also use it as a dummy subject in several constructions.

It is important to be on time for the meeting.
It is essential that you learn how to drive as we live in a village.
It is thought that Dr. Jameson will give a presentation.
It has been shown that paracetamol is helpful in such cases.

this

‘this’ is a demonstrative adjective/pronoun.

On the other hand, we use this to

refer back to a whole sentences that needs to be explained.
Simply reference a whole part of the sentence to further talk about something

Take a look at these examples to see the difference between using it and this in this way.

Examples

My computer is essential to me.
It is the one thing I can’t do without at work.

(It refers back to the computer only.)

Computers have become essential in the modern workplace.

This means that all employers must provide them to their employees.

(This refers back to the whole sentence because that sentence is thesis like, or needs to be explained.)

Our garden is pretty small.
It is big enough for us, though.

Our 2nd sentence continues with the paragraph, so we use ‘it’ as a reference.

Our garden gets a lot of sun year-round. This allows us to sit outside even in the winter.

(‘This’ now references the first sentence as a whole.)

This is used to introduce someone or something

This is my mother.
This is my village.

This refers to a specific thing just mentioned

This is their trip abroad.
She made lunch, and this made her late.

This is used to identify a specific person or thing close by or being indicated or experienced

This is the book I told you about.
Is this yours?