If your Postgres in docker container use pg_dumpall to backup:

docker exec -t your-db-container pg_dumpall -c -U postgres > dump_`date +%d-%m-%Y"_"%H_%M_%S`.sql

and then restore it:

cat dump_24-04-2021_20_50_17.sql | docker exec -i some-postgres  psql -U postgres

If you want to play with the current command we can run a new docker container with postgres, create table, and check how a command is working.

Start a container:

docker run --name some-postgres -e POSTGRES_PASSWORD=pass -d postgres

Go inside the container:

docker exec -it some-postgres bash

Start psql console:

psql -U postgres

Create table:

CREATE TABLE first_table (column1 int);

And then you can do anything you want :)