About iptables and firewall
 

I would like to know what is the difference between iptables and firewall?

Iptables (or Iptables/Netfilter, if you prefer) is the firewalling system used by Linux. So, in this context, you could say that they they were the same thing. Or, not.

For example, your firewall is the set of firewall rules that you run and that isn't Iptables, but your set of rules. And, if you use some other OS, you probably wouldn't want to be calling Iptables your firewall system, because it won't be.