What does an empty iptables mean?

Empty iptables rules simply mean you have no rules. Having no rules means the table “policy“ controls what happens to each packet traversing that table. The policy ACCEPT on each table means that all packets are allowed through each table. Thus, you have no firewall active.

You don’t have any rules set up. Take a look at the following iptables tutorial on how to add your rules.

You can add your SSH rule like so, which will allow all SSH through Port 22:

iptables -A INPUT -p tcp --dport 22 -j ACCEPT