How to block websites using Squid Proxy Server

If I have to give internet FROM PROXY SERVER to other pc then do I NEED ONE LAN CARD OR 2 LAND card ?? Thank you

It does not work guys, don't waste your time

not working

mam i used this setting on redhat 7 OS , i create multiple user on this system & block internet for users but users has going Firefox & system network setting & change proxy setting , please given me solution like ,How to restrict normal users from modifying network settings & also in browser to users not change proxy option in browser .

i am also facing the same problem every thing you have mentioned the i have configured according to that but sites are being still accessed by clients