Use "this"/"that" for singular ("this" = near, "that" = far) and "these"/"those" for plural ("these" = near, "those" = far).
Examples:
- This is my book.
- That is the school across the street.
- This cake tastes delicious.
- That idea seems unrealistic.
- These are my keys.
- Those are the mountains we climbed.
- These cookies are fresh.
- Those problems were solved yesterday.