Use This when you are refering to a thing, a person or an object near you. You can use This only in the singular form:
This is my friend Lucy.
I don’t know who put this coat here.
Have you seen this movie?
This dog is so cute.
Are you looking for this?
I didn’t know where to put this.
This book is really cheap.
Use These when you are refering to things, people or objects near you. You can use These only in the plural form:
These are my friends Jack and John. Did you know them?
I don’t know who put these shoes here.
Have you seen these movies?
These dogs and these cats are so cute.
Are you looking for these?
I didn’t know where to put these.
These books are really cheap.
Use That to refer to an object, a thing or a person far from you. You can use That only in the singular form:
That was an interesting idea.
Is that yours?
That is the girl I was talking about.
I didn’t like the color of that car.
I thought that wedding dress was gorgeous.
Did you know about that?
Use Those to refer to objects, things or people far from you. You can use Those only in the plural form:
Those were interesting ideas.
Are those yours?
Those are the girls I was talking about.
I didn’t like the color of those cars.
I thought those wedding dresses were gorgeous.
Did you know about those?
Also learn from Captain English about Color Idioms.