postgresql cannot connect as user to data server I'm very new to postgresql, I installed it on my windows machine, and created a few databases and users, and I'm trying to connect with one of the accounts I created. If I log in using the postgres account, and I list all users, I get the following: 

    postgres=# \du
                                         List of roles
   Role name    |                         Attributes                         |    Member of
----------------+------------------------------------------------------------+------------------
 oak_admin      | Superuser, Create DB                                       | {}
 oak_admin_r    | Cannot login                                               | {}
 oak_test_roles | Password valid until infinity                              | {}
 oak_test_user  | Password valid until infinity                              | {oak_test_roles}
 oak_user       |                                                            | {}
 oak_user_roles | Password valid until infinity                              | {}
 postgres       | Superuser, Create role, Create DB, Replication, Bypass RLS | {}


now I listed all the databases, and I got the following: 

postgres=# \l
                                                  List of databases
   Name    |  Owner   | Encoding |           Collate           |            Ctype            |   Access privileges
-----------+----------+----------+-----------------------------+-----------------------------+-----------------------
 oakdb     | postgres | UTF8     | English_United Kingdom.1252 | English_United Kingdom.1252 |
 postgres  | postgres | UTF8     | English_United Kingdom.1252 | English_United Kingdom.1252 |
 template0 | postgres | UTF8     | English_United Kingdom.1252 | English_United Kingdom.1252 | =c/postgres          +
           |          |          |                             |                             | postgres=CTc/postgres
 template1 | postgres | UTF8     | English_United Kingdom.1252 | English_United Kingdom.1252 | =c/postgres          +
           |          |          |                             |                             | postgres=CTc/postgres
 testdb    | postgres | UTF8     | English_United Kingdom.1252 | English_United Kingdom.1252 |
(5 rows)


With that I thought I had the users and I had the databases, so I should be able to connect. So I thought maybe I mistyped the password, so I altered the password to something very easy and tried that out, I got the following error: 

postgres=# ALTER USER oak_admin WITH PASSWORD  'very_easy';
ALTER ROLE
postgres=# \q

C:\Users\charb&gt;psql -U oak_admin
Password for user oak_admin:
psql: FATAL:  database "oak_admin" does not exist


Any ideas what am I doing wrong?
The default db name, if not provided, is the username. 
In this case oak_admin. 

Provide the database name you want to 
connect to using the --dbname= option. https://www.postgresql.org/docs/current/static/app-psql.html

In this example you should add --dbnsme=oakdb