No need to open Port 53. You aren't trying to provide DNS to the whole internet, right?
If you want to provide access to a specific service (SSH, HTTP, VPN), you need to lookup the port for that service, and only open those particular ports. You configure your router to open the port at your router, and forward all incoming traffic on that port to your server's internal IP address (the address it has on your internal network).
Make sure your server is patched, and firewall is turned on. It will get probed, a lot. On the server's firewall, you also need to open the specific port numbers associated with the service you plan to use.