Let’s run up the Docker image with an instance of PostgreSQL

docker run --name mypostgres -d postgres

Now, connect to the instance so we can create a database etc.

docker exec -it mypostgres bash

createdb -U postgres MyDatabase

Note: if you find this error message psql: FATAL: role “root” does not exist, you’ll need to switch to the postgres user, see below.

Switch to the postgres user (su substitute user).

su postgres
psql

At which point, we’re now in the psql application and can create databases etc.