vi /etc/squid/squid.conf
http_port 3128
acl  our_networks src 192.168.1.0/255.255.255.0
acl  deny_net  src 192.168.0.0/255.255.255.255.0
acl  deny-net dstdomain .example.com  #use to block a request from example.com domain

http_access allow our_networks
http_access deny deny_net
http_access deny deny-net

service squid restart or reload
squid -z 

visible_host client

enable 3128 via add a port in system-config-sucuritylevel

block example.com to access
acl examplenet dstdomain .example.com
http_access deny examplenet
f or safe part put 255.255.255.0 instead of 24  in squid setting
 
make sure example.com is listed in DNS server zone file.