No matter how hard core cli user you are it very often that you will need a GUI to perform some tasks just because, you can’t remember the commands or you want a better visualization (Firewall ports comes to mind).
SSH to your server and get root privileges.
Edit the repositories list
Scroll all the way to the end of the file and add
deb http://download.webmin.com/download/repository sarge contrib
Save and Exit
Download and install the key of the author
wget -q -O- http://www.webmin.com/jcameron-key.asc | sudo apt-key add
to update the repositories
and install webmin
apt install webmin
Now you can access the GUI interface by
https://<IP address or FQDN>:10000