squid.conf

auth_param basic program /usr/lib/squid3/basic_ncsa_auth /etc/squid3/passwords
auth_param basic realm proxy
acl authenticated proxy_auth REQUIRED
http_access allow authenticated

# Choose the port you want. Below we set it to default 3128.
http_port 3128

Then on the command line add your user:

htpasswd -c /etc/squid3/passwords username_you_like

and restart squid

service squid3 restart

service squid3 restart