Here you can allow or block traffic based on their port, IP address, protocol etc. For example, if you want to allow traffic to come in on TCP port 80, then you would simply put 80 in destination port, protocol TCP, leave everything else blank and press Add.
The rule will appear in the "Rules" table (which you can delete as well). And now, the device will received traffic on TCP port 80.
Similarly you can add multiple "iptables" rules. Most ports, by default, are blocked for incoming traffic except for what is allowed in the "Basic Firewall" setting. Here you can add/remove more ports and rules to allow/block incoming traffic.
The accepted / allowed rules would look like this, for e.g.:
