Demonstrative pronouns talk about the distance you are from specific objects.
Use this and these for objects that you can reach with your hands without getting out of your seat or moving your legs.
* For example, your computer is in front of you, you would use this. This is singular, these is plural.
(Example Sentences 1 and 2)
Use that and those for objects that are not close to you. Objects you cannot reach, you must get out of your seat to touch them, you would use that and those.
That is singular, those is plural.
(Example Sentences 3 and 4)
1. This computer is in front of me.
2. These pencils are in front of me.
3. That restaurant is in another city.
4. Those cars are down the street.