how Linux Network Configuration

Hello everyone,
I'm confused between iptables and route
-I have a fedora server that has 2 interfaces
External : p2p1

IP 192.168.110.110/24
Gw 192.168.110.1
DNS 192.168.110.1

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Internal : p2p2

IP 192.168.206.1/24
Gw 192.168.110.110
DNS 0.0.0.0

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-Client

IP 192.168.206.2/24
Gw 192.168.206.1
DNS 192.168.110.1

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The firewall is disable in the server
it pings from server device internal IP to client IP but doesn’t ping from server external IP to client IP
I did the iptables to allow the traffic in the forward chain

# iptables –t nat –A POSTROUTING –o p2p1 –MASQUERADE
#iptables –t nat –A PREROUTING –p tcp –d 192.168.110.1-–dport 80 –j DNAT -–to 192.168.206.1
#iptable  -A FORWARD –p tcp –d 192.168.206.1–-dport  80 –j ACCEPT

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also changed to enable sysctl net.ipv4.ip_forward=1
after doing these the client can access the internet..
now why do we need route?
And I wish I could use route but I didn’t understand it. I did like that on server but I really don’t understand it and I delete it before doing iptables

route add -net 192.168.206.1 netmask 255.255.255.0
    gw 192.168.110.1 p2p2

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please I am really confused between these if someone can help me. I need my network has more security..
and also I have another a question how can I use my external ip address as DNS.
Thanks guys!