If you have completed your installation of squid proxy server then you can see how your proxy server working and how it is handling caching or contents .
It is important to know whether squid server caching or not.
tail -f /var/log/squid3/access.log
Above command will monitor all incoming request and log them to /var/log/squid3/access_log file. Now if somebody accessing a website through browser, squid will log information.