Manual Installation (depending on your system)

Ubuntu/Debian

sudo apt update
sudo apt install postgresql

Rocky Linux/RHEL/AlmaLinux

sudo dnf install postgresql-server
sudo postgresql-setup --initdb

Start PostgreSQL

sudo systemctl enable --now postgresql

Create a database and user

sudo -u postgres psql

CREATE USER username WITH PASSWORD 'password';
CREATE DATABASE boards OWNER username;
\q

Use this value as DATABASE_URL in your .env file:

postgresql://username:password@localhost/boards

Additional Links:
4ga Boards Professional Hosting