Enter the psql command line by hitting
sudo -u postgres psql
Create the database by using the command. (don't forget to put your database name in place of: yourdbname )
CREATE DATABASE yourdbname;
Create a user with an encrypted password by using the command: (change youruser to your username and yourpass to your password. Password comes in the single comas)
CREATE USER youruser WITH ENCRYPTED PASSWORD 'yourpass';
Grant all privileges to your new user on your new database. (again provide your username and database name)
GRANT ALL PRIVILEGES ON DATABASE yourdbname TO youruser;