Today is Saturday. Saturday is today.
Yesterday was Friday. Friday was yesterday.
Tomorrow is Sunday. Sunday is tomorrow.
This month is September. September is this month.
Last month was August. August was last month.
Next month is October. October is next month.
This year is 2023. 2023 is this year.
Last year was 2022. 2022 was last year.
Next year is 2024. 2024 is next year.
This decade is the Twenties. The Twenties is this decade.
Last decade was the Teens. The Teens was last decade.
Next decade is the Thirties. The Thirties is next decade.
This century is the 21st. The 21st is this century.
Last century was the 20th. The 20th was last century.
Next century is the 22nd. The 22nd is next century.
Now are you clear about when what is?