Allow HTTP/HTTPS traffic with iptables

If you already have basic firewall, just add the following:

# ----------- BEGIN OF CUSTOM RULES -----------
#
# Allows HTTP and HTTPS connections from anywhere
-A INPUT -p tcp --dport 80 -j ACCEPT
-A INPUT -p tcp --dport 443 -j ACCEPT

#
# ------------ END OF CUSTOM RULES ------------

Now you can activate these rules as described here.