The ISPConfig docs recommend the auto-installer for Debian or Ubuntu. The commands below install a full stack using Apache. For Nginx, replace --use-apache with --use-nginx.
wget -O - https://get.ispconfig.org | sh -s -- --use-apache --unattended-upgrades
The installer prints the admin and database passwords when it finishes. Save them.
Open ports for the services you enabled. The guide lists, at minimum, these common ports:
Open https://YOUR_HOSTNAME:8080 and sign in with the admin credentials shown by the installer.