Access

well it will depends on the way you're going to implement proxy server in your network. anyway, basically browsers of your internet client is pointed to your proxy server. your proxy server tracks down the web access. instead of the client browser going directly to the intended website, the proxy server will do the surfing, and vice versa when the target website responds back. so there is no direct internet session, the proxy server breaks it and process it.

what allows the internet access to users? first is your proxy server ofcourse, other devices can be the firewall and the Internet router.

Rocky put it well. I would just add some of the advantages of using a proxy server to filter web access to your users. For example, if you're running a NT network, you can set up domain groups for users that you want to have Internet access. You can then add those groups to on the proxy server to allow them to get out to the internet.

You can also filter internet browsing based on protocol - for example to block FTP or instant messaging to users.

Hope that helps...