This, that, these and those are called demonstratives. We use a demonstrative when we want to talk about whether something is near or far from us and if the subject is singular or plural.
This car is nice (singular, near)
That car is nice (singular, distant)
These cars are nice (plural, near)
Those cars are nice (plural, distant)
Before the noun. – What are those people looking at?
Before the word 'one'. – This one is much cheaper than that one.
Before an adjective + noun. – These blue shoes would really suit you.
When it is clear what the noun is. – while eating ice-cream: This is delicious (you do not need to say, ‘This ice-cream is delicious’).
Now answer these demonstrative questions: