This/that - these/those

1. 'This', 'that', 'these' and 'those' are demonstratives. We use them to point to people and things. 'This' and 'that' are singular. 'These' and 'those' are plural. 
2. We use 'this' and 'that' with singular and uncountable nouns:
1. Try to repeat this exercise every morning ('exercise' is a singular noun)
2. What does this music make you think of? ('music' is an uncountable noun)
3. We use 'these' and 'those' with plural nouns:
1. You can use any one of these computers 
2. I need to paint those windows
4. We use 'this' and 'these' to point to things and people that are close to the speaker:
1. Shall I use this knife here? (the knife is next to me)
2. I’ll mail these letters on my way home (I'm holding the letters)
5. We use 'that' and 'those' to point to things and people which are distant from the speaker:
1. What’s in that bottle over there? (the bottle is far away)
2. Can you see those birds in the sky? (the birds are far away in the sky)
6. We often use 'this' with words describing time and dates like 'morning', 'afternoon', 'evening', 'week', 'month', 'year' to refer to ‘the one that’s coming’ or ‘the one we’re currently in’:
1. I’ll call you some time this evening (I'll call you the evening that's coming)
2. John is in Germany this week (John is in Germany in the week we're currently in)