We use the determiner 'this' (pl. 'these') when we speak about people, things or events that are present at the moment or near in time.
- This book is a best seller.
- Is this your car?
- Early this morning.
- These postcards are from Holland.
- I like these shoes.
We use the determiner 'that' (pl. 'those') when we speak about people, things or events that aren't near or present at the moment.
- Do you want that pair of shoes?
- That man is a doctor.
- Those children are very polite.
- Look at those clouds!
- How much are those apples?