It's basically enabling UFW

# installing and configuring ufw
sudo apt-get install ufw
sudo ufw status
sudo ufw allow 22/tcp
sudo ufw allow www/tcp
sudo uff allow 443/tcp
sudo ufw enable

This will block incoming requests except the SSH port, and ports 80 & 443. For server hardening, I also like updating all of the packages on a fresh install and installing fail2ban. I'll also typically update my SSH config (or verify it) that password authentication is disabled, so you can only use a SSH key to authenticate.

sudo apt update && sudo apt upgrade -y
sudo apt install fail2ban