psql: could not connect to server: No such file or directory

Oops, PostgreSQL is not running. Go back to the appropriate installation guide to see how to start it on your system. On Debian, it starts automatically after installation, so the above command produces the following result:

carla@xena:~$

psql: FATAL: role "carla" does not exist

Well, excuse me all to heck! But this really isn't a big deal, because PostgreSQL creates a default postgres superuser with no password. So you have to change to this user, and then create a new user account that you will use to administer the database. On Linux and Unix you need to gain rootly powers, like this: