Please add commands which you have found useful...

using psql (the Postgres shell)

Create a new Database:

CREATE DATABASE dbname;

To connect to ("use") a specific database

\c dbname

http://stackoverflow.com/questions/10335561/use-database-name-command-in-postgresql

Show (list of) Tables (for a given database):

\dt

http://stackoverflow.com/questions/769683/show-tables-in-postgresql