Once you’ve initially installed Postgres you should be able to connect almost immediately with psql -h localhost. This will put you inside your database to begin working. Of course the next step before doing anything else is to create a user account for yourself.
craig=# CREATE USER craig WITH PASSWORD 'Password';
New user craig is created with password Password.
Next step is to create a database and grant access to the user craig
craig=# CREATE DATABASE pgguide;
Now new database pgguide is created. Now we will grant access to craig.
craig=# GRANT ALL PRIVILEGES ON DATABASE pgguide to craig;
Now craig has all privileges on database pgguide. There are several different kinds of privilege: SELECT, INSERT, UPDATE, DELETE, RULE, REFERENCES, TRIGGER, CREATE, TEMPORARY, EXECUTE, and USAGE.
craig=# GRANT SELECT ON DATABASE pgguide to craig;
GRANT SELECT allows craig ONLY to do select query on database pgguide