sudo apt install postgresql
sudo -u postgres psql
\l      -- databases      \du  -- roles      \dt -- tables      \q -- quit

• Server config: postgresql.conf; who may connect: pg_hba.conf
• Listen only where needed: listen_addresses = 'localhost,192.168.10.40'
• In pg_hba.conf use scram-sha-256, restrict by subnet, never trust on a network line
• One role per application with only the rights it needs:

CREATE ROLE app LOGIN PASSWORD '…';
CREATE DATABASE appdb OWNER app;