You can check the attributes of a given user in psql as follows:
pguser=# du alice
This gives the following output:
List of roles Role name | Attributes | Member of-----------+------------+----------- alice | Create DB | {}
The CREATE USER and CREATE GROUP commands are actually variations of CREATE ROLE. The CREATE USER username; statement is equivalent to CREATE ROLE username LOGIN;, and the CREATE GROUP groupname; statement is equivalent to CREATE ROLE groupname NOLOGIN;.