Firewall Rules and Variables =/

i'm new to iptables and i found a sample firewall script and i was
hoping someone could break down how variables run within the script.
if anybody can point out what the variables are doing and just give a
little insight as to whats going on in this script i would really
appreciate it. i understand the basics about chains (forward, input,
output) and jump actions. but what the hell does the "For" command do,
and why is it seperated into public and private services, and how can
the rules tell? if any other new guys are lookin at this i found a
good site to get a basic picture of how things work:
http://wiki.centos.org/HowTos/Network/IPTables ; thanks guys and have
a great day.

#!/bin/bash
# Rules for sample firewall

.. /etc/init.d/functions
.. /etc/sysconfig/firewall/config

# VARIABLES
SERVER_NAME="samplefirewall"
SERVER_ADMIN_IP="192.168.1.5"
SERVER_IP_LIST="${SERVER_ADMIN_IP} 192.168.1.2 192.168.1.3"
SOURCE_RANGES_ALL="192.168.1.4"

RETVAL=0

start () {

echo -n " ${SERVER_NAME}: "

# Create forward_${SERVER_NAME}_in jump in forward_in table
${IPTABLES} -N forward_${SERVER_NAME}_in
for i in ${SERVER_IP_LIST}; do
${IPTABLES} -A forward_in -d ${i} -j forward_${SERVER_NAME}_in
done


# forward_${SERVER_NAME}_in rules
# Public Services
${IPTABLES} -A forward_${SERVER_NAME}_in -d ${SERVER_ADMIN_IP} -
p tcp -m multiport --dports
80,1111,1935,1755,554,110,443,993,995,5818,5001 -j ACCEPT
${IPTABLES} -A forward_${SERVER_NAME}_in -d 192.168.1.2 -p tcp -
m multiport --dports 80,443 -j ACCEPT
${IPTABLES} -A forward_${SERVER_NAME}_in -d 192.168.1.3 -p tcp -
m multiport --dports 80,443 -j ACCEPT
echo -n "public "


# Private Services
for i in ${SOURCE_RANGES_ALL}; do
${IPTABLES} -A forward_${SERVER_NAME}_in -s ${i} -d $
{SERVER_ADMIN_IP} -p tcp -m multiport --dports
20,21,22,80,443,5050,818,9001 -j ACCEPT
done

echo "private "
echo_success
echo

RETVAL=$?
return ${RETVAL}

}


stop () {

echo -n " ${SERVER_NAME}: "

# Remove references, flush table, then delete it
for i in ${SERVER_IP_LIST}; do
${IPTABLES} -D forward_in -d ${i} -j forward_${SERVER_NAME}_in
done
${IPTABLES} -F forward_${SERVER_NAME}_in
${IPTABLES} -X forward_${SERVER_NAME}_in

echo_success
echo

RETVAL=$?
return ${RETVAL}

}

case "$1" in
start)
start
;;
stop)
stop
;;
restart|reload)
stop
start
;;
*)
echo $"Usage: $0 {start|stop|restart|reload}"
exit 1
esac

exit $?