THIS- THESE / THAT - THOSE

Why do we use this and these?

We use this (singular) and these (plural) as pronouns:

- to talk about people or things near us:

This is a nice cup of tea.
Whose shoes are these?

- to introduce people:

This is Janet.
These are my friends, John and Michael.

WARNING:
We don’t say These are John and Michael.
We say This is John and this is Michael.

- to introduce ourselves to begin a conversation on the phone:

Hello, this is David, Can I speak to Sally?

Why do we use that and those?

We use that (singular) and those (plural):

- to talk about things that are not near us:

What’s that?
This is our house, and that’s Rebecca’s house over there.
Those are very expensive shoes.

- We also use that to refer back to something someone said or did:

• - Shall we go to the cinema?
  - Yes, that’s a good idea.
• - I’ve got a new job.
  - That’s great.
• - I’m very tired.
  - Why is that?

this, these, that, those with nouns

We also use this, these, that and those with nouns to show proximity

We use this and these for people or things near us:

We have lived in this house for twenty years.
Have you read all of these books?

… and that and those for people or things that are not near us:

Who lives in that house?
Who are those people?

http://www.englishexercises.org/makeagame/viewgame.asp?id=4617

http://www.englishexercises.org/makeagame/viewgame.asp?id=4102

http://www.agendaweb.org/grammar/demonstratives-exercises.html