how to configure proxy server(squid) to certain link

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http://serverfault.com – I'm a beginner in this area, please bare with me if my request is messy. I need to configure a proxy server 1) which will allow my clients to connect to my proxy server then 2) they will be able to see a login page. when i asked some IT gurus they told me "configure the forwarding url in proxy". how do i achieve this? what kind of proxy i should use ? Please help, thanks in advance. (HowTos)