➥ A simple iptables firewall script to block all ports except port 80 and give port 22 to certain ip's

This simple script is very useful and very simple and will give you the basics of what you can do with linux iptables firewall.

Make a file:
pico /root/firewall.sh

Paste all the info and correct the ip addresses with you owns.
iptables -P FORWARD DROP # we aren't a router
iptables -A INPUT -m state --state INVALID -j DROP
iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A INPUT -i lo -j ACCEPT
iptables -A INPUT -s -j ACCEPT
iptables -A INPUT -s -j ACCEPT
iptables -P INPUT DROP # Drop everything we don't accept
iptables -A INPUT -p tcp --dport 80 -j ACCEPT

Give it some permissions
chmod 777 /root/firewall.sh

And run the script.

Now this was tested in ubuntu 17.04 but if you have problems with the destination of the iptables you can try adding sbin/iptables.
You can list all the active iptables rules with the command
iptables -L

-L is capital.