To install Webmin on Debian Linux 9.5 you can follow these commands, (accept any prompts)
wget http://prdownloads.sourceforge.net/webadmin/webmin_1.890_all.deb
apt-get install perl libnet-ssleay-perl openssl libauthen-pam-perl libpam-runtime libio-pty-perl apt-show-versions python
dpkg --install webmin_1.890_all.deb
That's it, basic setup is now complete.
You can now access your server using the default https:// {youIPaddressOrServerAddress} :10000
Be sure to properly secure your server before putting it into production.
In some cases you may need to clear the command line history in Linux for security. Here is the command.
history -cw