Well, *usually* it starts automatically and remains in the background.
This is the normal way to start the service (or replace 'start' with 'stop' to stop it):
sudo service postgresql start
Or to manually start, try something like this:
/usr/lib/postgresql/9.5/bin/postgres -D /var/lib/postgresql/9.5/main -c config_file=/etc/postgresql/9.5/main/postgresql.conf
The tutorial asks me to do sudo bash, but that gave me this: [sudo] password for postgres:
But, the postgres password doesnt work, I even changet it using ALTER USER.
What can I do?