What am I doing with iptables?

I've only used ufw and just now I had to run this command to fix an issue with docker.sudo iptables -I INPUT -i docker0 -j ACCEPTI don't know why I had to run this to make curl work.

So, what did I exactly just do?This is behind my house router which already has reject input from wan, so I'm guessing it's fine, right?

I'm asking since the image I'm running at home I was previously running it in a VPS which has a public IP and this makes me wonder if I have something open there without knowing :/

ufw is configured to deny all incoming, but I learnt docker by passes this if you configure the ports like 8080:8080 instead of 127.0.0.1:8080:8080. And I confirmed it by accessing the ip and port.