For a very basic setup you need to edit the file /etc/squid/squid.conf and add two lines. First search for the second occurance of "Recommended minimum configuration and add an acl for your network below the acl CONNECT method CONNECT line
acl mynetwork src 192.168.2.0/24
Then search further down the configuration file for the line containing INSERT YOUR OWN RULE(S) HERE. Add the following line above the localhost access rule
http-access allow mynetwork
Restart the squid service. Set your browser to use port 3128 on localhost and try going to an external website.