The docs could be more helpful

[Pumpapa]

Dependencies are Elixir, Phoenix, PostgreSQL, but Phoenix depends on Postgresql so the order isn't right
The Phoenix docs say to install mix local.hex but that doesn't work
I skip that and continue on your instructions, and mix deps.get offers to install hex. Goodie.
But then: mix ecto.create installs a lot but fails at

...
14:04:16.964 [error] GenServer #PID<0.7212.0> terminating
** (Postgrex.Error) FATAL 28P01 (invalid_password): password authentication failed for user "postgres"
    (db_connection 1.1.3) lib/db_connection/connection.ex:163: DBConnection.Connection.connect/2
    (connection 1.0.4) lib/connection.ex:622: Connection.enter_connect/5
    (stdlib 3.13) proc_lib.erl:226: :proc_lib.init_p_do_apply/3
Last message: nil
State: Postgrex.Protocol
** (Mix) The database for RealWorld.Repo couldn't be created: FATAL 28P01 (invalid_password): password authentication failed for user "postgres"

Presumably I should have created the postgres user, but this isn't mentioned anywhere.
But I rarely use postgres, so I wouldn't know where to begin

[bartvanderwal]

As mentioned in my issue #45 the default username for postgres on macos is your macos username.

If you're running windows, this might be different, check the postgres docs. I DID get a slightly different error message, so perhaps your username is correct, but besides changing the username, you could also try changing your password in the config.exs file. For instance set it to empty as I did (which is default on other systems as well. Or — of course — to the password you entered on install — if any.