How does the UNNEST operator work in SQL?

Question

SQL

Good afternoon.

I can't figure out how the UNNEST operator works.
Can you link to a good description or describe how it works step by step?

Thanks

Answer 1

Description here https://www.postgresql.org/docs/13/functions-array.html
Well, for example here https://habr.com/ru/post/280912/ Example 2 about it