Webmin allows you to manage deployment packages and perform configuration settings in a easy way by providing a web interface at port 10000 in a Raspberry Pi. This application also provides easy options to start an application at boot without writing lengthy configuration scripts.
Detailed installation steps are available at webmin site. Follow those steps to install webmin application in Raspberry Pi
Once you have successfully completed the installation, you can access the webmin application at https://127.0.0.1:10000 ( Note that this is https not http) by providing the username password of “pi” account
After installation, you can navigate to source.list (leafpad /etc/apt/sources.list) and comment the 2 new source repositories that you have added for webmin