Normally, your browser requests web pages directly from the web site.
When you use WebMask, you set your browser up to request web pages from WebMask. Then WebMask in turn requests these pages from the web site. This is called using WebMask as a proxy.
It is because WebMask sits between your browser and every web site that it is able to remove adverts, and improve your privacy.
A proxy runs on a certain computer (or host) which has a name, for example www-cache.demon.co.uk. It also connects via a port; either port 80, port 3128, or port 8080 is usually used for proxies. The host and the port allow the web browser to find the proxy.
WebMask runs on your own machine, so the host address is the internet name of your own computer, or the number 127.0.0.1 which always refers to your own computer. WebMask uses port 8080 by default.
When you configure your browser to use WebMask as a proxy, you will tell it to use machine 127.0.0.1 and port 8080.
Sometimes your browser will already be configured to use a proxy. This might be because you work inside a company firewall, and you need to use a proxy to access the rest of the internet. Or it might be because you use a caching proxy run by your Internet Service Provider, which speeds up access to web pages.
Because you now need to tell your browser to use WebMask as a proxy, your browser can no longer refer to another proxy. Instead you configure WebMask to use that proxy - you are chaining proxies.
So, if your browser was already using a proxy, you have to remember the host and the port that it was using. Then you need to put this information into WebMask. Now when your browser requests a web pages, it asks WebMask for it. WebMask in turn requests the page from your proxy (except for any filtered adverts), which in turn requests it from the web site.